Bioassay tests were conducted with twenty three pesticides taking a fresh water teleost, Saccobranchus fossilis as test animal. Acute toxic ranges and LC50 values for 7 organochlorine, (thiotox, endosulfan, heptachlor, chlordane, aldrin, lindane and BHC), 14 organophosphorus (zolone, ekalux, diazinon, rogor, DDVP, malatox, sumithion, ekatin, metasystox, malathion, phosvel, dipterex, formothion and abate) and 2 carbamate pesticides (carbofuran and sevin) were determined using static testing procedures for a period of 24, 48, 72 and 96 h both by graphical interpolation and probit analysis. 95% fiducial limits and heterogeneity factors X2) only for 96 h LC50 values were calculated. The relative potency of all the 23 pesticides have been calculated with respect to abate. It was in the decreasing order from organochlorines (1–7), to organophosphorus (8–21) and carbamate pesticides (22, 23), respectively. The presumable safe concentrations were computed, using 0.021, 0.024 and 0.026 as arbitrary application factors based on other species for organochlorines, organophosphorus and carbamate pesticides, respectively.