Twenty-five pesticides used in the production of rice and soybeans in Texas were tested in the laboratory to determine their toxicity to the eggs of Psorophora columbiae. A reduction in hatching rate occurred when eggs were treated with a herbicide formulation containing thiobencarb and with one containing a tank mixture of propanil and molinate. A carbaryl formulation induced hatching of eggs prior to their exposure to the hatching stimulus. Reduced survival to second instar of larvae hatching from treated eggs was observed with insecticide formulations of acephate, carbofuran, malathion, methyl parathion and toxaphene; a fungicide formulation of triphenyltin hydroxide and the tank mixture of the herbicides, propanil and molinate.