In vitro fungicidal properties of cecropin B and dermaseptin were explored using nongerminating and germinating conidia from Aspergillus flavus, A. fumigatus, A. niger, Fusarium moniliforme and F. oxysporum. Cecropin B produced LD50 values for germinating A. flavus, A. fumigatus and A. niger conidia of 3.0, 0.5 and 2.0 μM, respectively, while dermaseptin gave LD50 values of 4.0, 0.05 and 2.0 μM, respectively. Cecropin B produced an LD50 value of 0.2 μM for non-germinating F. moniliforme and F. oxysporum conidia, while dermaseptin did not reduce either as much as 50% at any level tested. LD50 levels for CB were 0.2 and 0.1 μM, respectively, for germinating F. moniliforme and F. oxysporum conidia. Dermaseptin was less effective, giving LD50 values for germinating F. moniliforme and F. oxysporum conidia of 0.3 and 0.8 μM, respectively. Neither peptide reduced conidial viabilities of non-germinating Aspergillus spp. Physicochemical studies indicated cecropin B and dermaseptin bound to ergosterol and cholesterol, conidial wall constituents, but not to chitin or β-1,3-glucan.