Two soil cyanobacterial species were used to investigate the factors affecting the toxicity of two common used insecticides, larvin (Dimethyi N,N-[thiobis (methyl amino carbonyloxy)]-bis-(ethanimidothioate) and sevin (1-Naphthyl N-methylcarbamate) to soil microflora. The heterocystic filamentous Anabaena subtropica Gardner and Anabaena variablis Kutzing ex.Born. et Flah., were exposed to four concentrations (5,15,20 and 40 mg L^-1) of larvin and sevin. Differential growth effects were observed among the two cyanobacterial species exposed to all insecticides concentrations. Selected properties of the test cyanobacteria (chl a, dry weight, O₂ evolution, nitrogenase activity, total soluble proteins, total lipids and fatty acid contents of the total lipids) were measured and examined for their relationship to larvin and sevin sensitivity. Strong inhibiting percentages in all measured parameters in both Anabaena species under the different pesticides concentrations of larvin and sevin except the total lipids were recorded, suggesting that these attributes to the potential hazard of these insecticides to soil microflora and subsequently natural ecosystems.