The effect of tamoxifen (ICI-46474) (alpha-[4-(beta-N-dimethylamino ethoxy)-phenyl]alpha'-ethyl trans stilbene on estrogen cytosolic receptor was observed in different parts of fallopian tube and uterus of rabbits during ovum transport. Tubal segments viz. ampulla (A), ampullary isthmic junction (AIJ), isthmus (I), uterine isthmic junction (UIJ) and uterus (U) were studied during the passage of ovum. Significant differences were observed in normal, drug treated and pregnant animals at 14, 24, 34, 48, 72, 144 and 168 h. In treated animals during 14 h post-coitum (p.c.) to 34 h p.c. the ampullary cytosol receptor concentration increased and suddenly decreased at 48 h p.c. whereas from 72 h p.c. to 144 h p.c. it increased gradually. Tamoxifen accelerated the rate of egg transport decreasing tubal cytosolic receptors at 48 h p.c. However, beyond 48 h p.c. receptors increased till 144 h p.c. Results suggest that tamoxifen modulated tubal cytosolic estrogen receptors during egg transport and prevents pregnancy.