Abstract: Condensation of chlorides of substituted pyrazine-2-carboxylic acids with ring substituted anilines yielded a series of anilides of 6-chloropyrazine-2-carboxylic, 5-(1,1-dimethylethyl)-pyrazine-2-carboxylic or 6-chloro-5-(1,1-dimethylethyl)pyrazine-2-carboxylic acids. Products were tested for their photosynthesis-inhibiting activity. The most active inhibitor of oxygen evolution rate in spinach chloroplasts was 3,5-bis(trifluoromethyl)anilide of 6-chloropyrazine-2-carboxylic acid (IC50 = 0.026 mmol dm-3), the most active antialgal compound was 3-methylanilide of 6-chloro-5-(1,1dimethylethyl)pyrazine-2-carboxylic acid (IC50 = 0.063 mmol dm-3). The elimination of phenolic group in the benzene moiety led to an decreased photosynthesis-inhibitory activity.