The effect of atrazine (2-chloro-4-ethylamino-6-isopropylamino-.s-triazine) on growth ofSclerotium rolfsiiandTrichoderma viridewas studied in liquid culture. The fungi were grown in Czapek solution containing 0, 8, 20, 40, and 80 μg of the herbicide per milliliter, and growth responses were measured at intervals of 3–5 days after inoculation. Mycelial dry weight ofS.rolfsiiwas little affected at concentrations below 40 μg/ml, but was decreased at the higher concentrations. Total mycelium produced byT.viridewas greater with all atrazine treatments than in the control. ForS.rolfsii, the efficiency of utilization (economic coefficient) of glucose, inorganic P, and NO3-N with atrazine at 8 μg/ml was slightly higher than that of the control, but was significantly reduced at higher concentrations. Values for glucose utilization efficiency inT.virideincreased with herbicide at 8 and 20 μg/ml, then decreased considerably at other concentrations, but remained higher than the control; a similar pattern was revealed for P and NO3-N utilization. Titratable acidity in the medium increased for both fungi with increased atrazine concentration.