Registry members participate 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.

Join the Registry

• Identical and fraternal twins (mixed-gender or same-gender pairs) aged 18 and over in the San Francisco Bay Area: Register online or call SRI 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.) Youths aged 17 and younger comprise 15% of total registrants.

Current Studies (recruiting now)

• Year 4 of a flu vaccine study, conducted in partnership with Stanford University

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

Learn more about current studies

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

About the Registry’s 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 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.

More Information

Read about the twin community in our newsletters, and visit our Facebook page.

For more information on twins research and twin registries, watch these presentations by Dr. Gary Swan:

• Twins: Unlocking the Secrets of Nature-Nurture Interactions Part 1 Part 2