Comparative tests were conducted on Pythium ultimum and Phymatotrichum omnivorum to determine if an alternative mode of action exists for the two triazole fungicides under investigation. The accepted mode of action of penconazole (Tapas^®) and propiconazole (Tilt^®) is the inhibition of ergosterol biosynthesis in fungi (1,4,5,6). P. ultimum which does not synthesize or require sterols for vegetative growth has shown "moderate sensitivity" to Topas in greenhouse and in vitro tests (3). The results show that only Topas at minimum inibitory concentrations caused the accumulations of possible "sterol-like' or pentacyclic terpenoid compounds in P. ultimum, which eluted out in the sterol range when utilizing high performance liquid chromatography. Both fungicides at minimum inhibitory concentrations caused the accumulations of lanosterol as well as ergosterol in P. omnivorum. Although both sterols accumulated in treated mycelium, of P. omnivorum, the percent of these sterols in the total lipid fraction is higher 3 hours post treatment relative to the control while this same percentage was lower 12 hours post treatment relative to the control.