The 96 h LC50 values of carbaryl, methyl parathion individually and equitoxic of both were 19.99, 10.00, and 16.68 ppm respectively. Animals exposed to sublethal levels of carbaryl and methyl parathion individually and in combination significantly reduced the rates of feeding, absorption, and conversion and increased oxygen consumption and surfacing frequency. Methyl parathion was more toxic than carbaryl in individual concentration and in combination produced synergistic and antagonistic effects.