Twins have long held a special place in medical science as a source of insight into human behavior and genetic links. As a part of its scientific research and efforts to discover more about human behavior, SRI International's Center for Health Sciences established the Northern California Twin Registry in 1995, now Twin Research Registry at SRI International. There are currently more than 2,800 adult twin registrants active in the Registry. Fifteen percent (15%) of these twins are youths under 18.

Registry members have participated in studies focusing on the pharmacokinetics of nicotine, metabolism of commonly used medications, genetic susceptibility to cancer-causing chemicals, and sleep patterns in young twins.

Do you know any twins?

You can earn money just by referring a pair of identical or fraternal twins to our Registry. If they both join, we'll send you $25.

Become a Member of the Twin Research Registry™ at SRI International

Identical and fraternal twins (mixed-gender or same-gender pairs) aged 18 and over in the San Francisco Bay Area: We invite you to REGISTER ONLINE or call us at 1-800-SRI-TWIN (1-800-774-8946). By registering, you will be eligible to be invited to participate in studies. Most studies offer payment for your participation.

Identical and fraternal twins (mixed-gender or same-gender pairs) aged 17 and under in the San Francisco Bay Area: Parents or guardians, please call 1-800-SRI-TWIN (1-800-774-8946) to register your twins in the Twin Research Registry at SRI International. (As a precaution, we ask that you do not register a minor online.)

Learn about the Registry

Read about the twin community in our newsletters.

For more information on twins research and twin registries, watch these videos about "Twins: Unlocking the Secrets of Nature-Nurture Interactions": Background on twins research and an overview of Twin Registries from Dr. Gary Swan's talk at Cafe Scientifique Silicon Valley.

Current Studies (recruiting now)

• A flu vaccine study, conducted in partnership with Stanford University
• A Zoster (shingles) vaccine study, conducted in partnership with Stanford University

Past Studies

• In partnership with Stanford University, we examined the genetic and familial aspects of pain sensitivity
• Examination of the renal clearance of the commonly used prescription medication metformin (used in treatment of diabetes) in identical and fraternal twins to determine the role of heredity
• Comparison of the pharmacokinetics of the medication digoxin (a heart regulator) in identical and fraternal twins to determine whether inter-individual variability is due to genetic factors
• Examination of the extent to which genetics and environment affect sleep in children
• Investigation of the role of genetics in response to cancer-causing agents
• Investigation of whether the predisposition for cigarette smoking is related to how fast the body eliminates nicotine
• Testing of a biometric recognition technique to capture three-dimensional facial images in identical twins

Our Name and Logo
The name of the Twin Research Registry™ at SRI International, reflects our goals to be progressive, inclusive, and innovative in our research efforts.

Our new logo was designed to represent the individuals and twin pairs that are so important to our research studies. The logo originated from the symbol for "person" in Chinese characters. The design symbolizes multiplicity, connection, bridging, and networking. It also hints at SRI’s Northern California location, but it flows openly to reach out to the rest of the world. The combination of colors is meant to evoke trust, confidence, wisdom, dignity, enthusiasm, fascination, and strength.

The Twin Research Registry at SRI International is an active registry of twins of all ages and backgrounds, fraternal and identical, who are interested in learning more about twins and to participate in research studies to help advance science.

Contact Us
Inquiries or comments on the Registry are welcome and can be directed to

Center for Health Sciences
SRI International
333 Ravenswood Avenue
Menlo Park, CA 94025

twin@sri.com

Phone: 1-800-SRI-TWIN (1-800-774-8946)
Fax: 650-859-5099