Abstract: A series of substituted 2-amino-N-phenylbenzamides (1) and 3-phenyl-1,2,3-benzotriazin-4(3H)-ones (2) was synthesized and evaluated in vitro for their antimycobacterial, antifungal, and photosynthesis-inhibiting properties. Some compounds 1 exhibited good activity against Mycobacterium tuberculosis as well as against atypical strains of mycobacteria. The introduction of chloro substituent into position 5 improved the antimycobacterial activity of 1. Most 5-chloro derivatives 1 were more active against atypical strains than INH. The most active derivative was 2-amino-5-chloro-N-(4-sec-butylphenyl)benzamide. A moderate antifungal activity against Trichophyton mentagrophytes was found for some 1, but significant activity against the other tested fungal strains was not observed. In general, the ring closure in 3-phenyl-1,2,3-benzotriazin-4(3H)-ones (2) led to decrease or loss of antimycobacterial as well as antifungal activity. The photosynthesis-inhibiting activity of 2 concerning inhibition of oxygen evolution rate in spinach chloroplasts was investigated. The relatively low photosynthesis-inhibiting activity of 2 is probably a consequence of their low aqueous solubility causing a restricted passage of the inhibitor through the hydrophilic regions of thylakoid membranes.