Various kinds of lipophilic analogues of isonicotinic acid hydrazide (Isoniazid) were synthesized and in vitro explored in a search for antimycobacterial agents with extended activity spectrum against pathogens responsible for the AIDS-associated diseases. The primary in vitro screening showed that a) isonicotinoylhydrazones 1a, 1b, 1d, 1e are more active than the parent drug against non-tubercular mycobacteria (MIC ranging between 0.5 and 4 micrograms/ml), b) isonicotinohydrazides 6b and 6e display interesting antibacterial activity on some Gram + and Gram-strains, and c) trifluoromethyl-containing compounds 1a and 2c inhibit the growth of several human tumor cell lines at doses between 10(-5) and 10(-6) M. On the contrary, none of the tested analogues significantly counteracts the cytopathogenicity induced by HIV and HSV viruses.