Genetically different strains of laboratory mice vary dramatically in their sensitivity to estrogen, report UC Davis researchers in the Aug. 20 issue of the journal Science.

The findings by reproductive geneticist Jimmy Spearow and reproductive endocrinologist Marylynn Barkley call into question the validity of current laboratory-animal-based safety tests of estrogenlike chemicals and suggest that an individual's genetic makeup should be considered when prescribing estrogen and related hormones for medical purposes.

The U.S. Environmental Protection Agency is preparing to screen thousands of pesticides and industrial chemicals for several endocrine-disrupting effects. Previous studies have indicated that estrogenlike endocrine disruptors found in the environment can cause decreased sperm counts, deformed genitals, aberrant mating behavior and sterility in wildlife.