Diethylstilbestrol (DES) lowers enzyme efflux from isolated mouse skeletal muscle. It also lowers the high serum enzyme activities in Duchenne's muscular dystrophy. We have begun a systematic study of DES congeners, to identify those portions of the DES molecule which are critical to these effects, and to tailor a molecule which might have fewer feminizing effects. The first compound tested was the 3,3' diallyl derivative of DES (DAS). It was selected because previous reports indicated that it was as anabolic as DES, but only 1/10 to 1/30 as estrogenic. Doses of 20, 100 and 250 microgram/mouse/day were administered in 0.05 ml sesame seed oil vehicle to C57BL/6 mice. Control animals received only the vehicle. In contrast to DES which has consistently reduced muscle enzyme efflux 30-50%, DAS was inert. The substitution of the two allyl groups in the 3 and 3' positions blocks access to the neighboring ethyl groups and partially covers the two phenolic hydroxyl groups of DES. This suggests that these molecular sites have pertinence to the reduction of enzyme efflux from mouse skeletal muscle by DES, and possibly the reduction of the high serum enzyme activities in Duchenne's muscular dystrophy.