SUMMARYOospore distribution patterns in pairings between compatible isolates ofPhytophthora capsicisuggested mutual induction of oospore formation. Oogonia and oospores formed near the A2colony were smaller than those developing near the A1colony, suggesting that the smaller bodies were A2products and the larger bodies were formed by A1. This interpretation was confirmed in pairings physically separated by polycarbonate membranes. Significantly more oospores were produced in synthetic medium containing Difco Bacto agar as compared to Difco Noble agar, Difco purified agar or SeaKem agarose.