Twenty-six trichothecene mycotoxins produced byFusarium sporotrichioides(MC-72083) andFusarium sambucinumwere screened for relative cytotoxicity in cultured baby hamster kidney (BHK-21) cells. The relative cytotoxicity was measured as LC100. The most cytotoxic trichothecenes were T-2 toxin (5 ng/ml) and the recently isolated 4-propanoyl HT-2 (5 ng/ml) and 3′-hydroxy T-2 toxin (5 ng/ml). T-2 tetraol (1 × 104ng/ml), 8-β-hydroxytrichothecene (1 × 104ng/ml), sporotrichiol (2 × 104ng/ml), 8-oxodiacetoxyscirpenol (6 × 104ng/ml) and 8-acetyl T-2 tetraol (1 × 105ng/ml) were the least toxic of the regular trichothecenes. None of the modified trichothecenes or the apotrichothecene were very cytotoxic: 8-β-hydroxysambucoin (2 × 103ng/ml), FS-1 (5 × 103ng/ml), 8-α-hydroxysambucoin (8 × 104ng/ml) and trichotriol (1 × 105ng/ml). The modified trichothecenes, FS-2 and FS-3, were not toxic even at 1 × 105ng/ml. The baby hamster kidney cell bioassay proved to be a very sensitive and reproducible means of screening new trichothecene mycotoxins for relativ