The in vitro evaluation of antibacterial, antifungal and genotoxic activities of some 1-acyl-3-acylimino-2,1-benzisothiazolines is described. Compounds 55, 58, 60 and 62 exhibited a selective antibacterial activity. Compounds 1, 2, 30, 59 and 63 were active against Botrytis cinerea, compounds 6, 20, 39 and 54 against Pythium irregulare. DNA-damaging activity in the Bacillus subtilis rec-assay was demonstrated for compounds 45, 46, 54, 55, 57 and 61. By the Salmonella-microsome assay, genotoxic activity was confirmed and demonstrated also for compounds 10, 28, 29, 40, 44, 47-53, 56, 58-60, 62 and 63. Relationships between structure and genotoxic activity showed that all compounds containing an aromatic -NO2 group, except compound 27, were active. Among derivatives containing a -CH2Cl group in the acylic chain, only compound 40 showed mutagenic activity.