Endrin and malathion effects on survival, growth, and reproduction of flagfish were determined in a flow-through system. Endrin chronic effects on first-generation growth and reproduction occurred only at 0.3 microgram/l, the highest concentration tested. The mean endrin residues in the first-generation fish at 65 days were about 15,000 times the water concentration in all concentrations tested. Malathion concentrations of 31.5 microgram/l and 24.7 microgram/l, the highest concentrations tested, had detrimental effects on first-generation survival. During the same period malathion concentrations as low as 10.9 microgram/l significantly affected growth. Neither insecticide, at the concentrations tested, had any detectable effects on the second generation during a 30-day exposure period. Acute toxicities to juvenile fish were also determined in the same flow-through system. The 96-hr LC50's were 0.85 microgram/l for endrin and 349 microgram/l for malathion.