ABSTRACT Three newly synthesized non-steroidal derivatives of chalcone (benzalacetophenone), viz., 2′-chloro-4:4′-difluorochalcone (CH-4), 2′-chloro-3:4-methylenedioxy-4′-fluorochalcone (CH-6) and 2′-hydroxy-3:4-methylenedioxy-4′-fluorochalcone (CH-8) were evaluated for their oestrogenicity in the mouse and were found to possess a statistically highly significant (P < 0.001) uterotrophic effect at a dose of 1.0 mg/mouse. Of the three compounds CH-6 was the most potent. In comparison with oestradiol-17β, CH-6 proved to have a very low oestrogenic activity; however, it caused a highly significant increase in the mouse uterine weight at a dose of 0.1 mg/mouse, while a maximal effect was produced at a dose of 1.0 mg/mouse. CH-6 was investigated for its post-coital antifertility effect in the mouse. At a dose of 1.0 mg/mouse and with the experimental regimen used CH-6 inhibited implantation in the mouse. When CH-6 was administered to 30-day old male mice for 5 consecutive days doses of 0.5 mg, 1.0 mg and 2.0 mg/mouse caused a highly significant decrease in the weight and size of the testes and seminal vesicles.