Acute (96-hr) flow-through toxicity tests, chronic (entire life-cycle) tests, and bioconcentration studies were conducted on selected estuarine animals with the insecticides, EPN, and leptophos. In the EPN acute toxicity tests, the test animals and their 96-hr LC50 values were: Mysidopsis bahia, 3.44 micrograms/l; Penaeus duorarum, 0.29 micrograms/l; Cyprinodon variegatus, 188.9 micrograms/l; Lagodon rhomboides, 18.3 micrograms/l; and Leiostimus xanthurus, 25.6 micrograms/l. Test animals and 96-h LC-50 values for leptophos were M. bahia, 3.16 micrograms/l; P. duorarum, 1.88 micrograms/l; and L. xanthurus, 4.06 micrograms/l. In separate chronic tests, M. bahia were exposed to EPN and leptophos. Significant (alpha = 0.05) mortality and fewer young were produced in 4.13 micrograms/l EPN. In the leptophos chronic test, significant mortality occurred in concentrations > or = 3.63 micrograms/l and fewer young were produced in concentrations > or = 1.77 micrograms/l. L. rhomboides, exposed to EPN in a 26-day uptake study, bioconcentrated the insecticide 707 X that measured in the exposed water. The results indicate that if either contaminated an estuarine environment in concentrations > or = 1.0 micrograms/l, the most profound adverse effects on crustaceans and possibly fishes would result from acute toxicity, rather than from chronic toxicity or bioconcentration of the chemicals.