A continuous flow procedure was developed for evaluating effects of insoluble and volatile organics on embryo-larval stages of fish. Test compounds were selected for different combinations of solubility and volatility and included aniline, atrazine, chlorobenzene, chloroform, 2,4-dichlorophenol, 2,4-dichlorophenoxyacetic acid, dioctyl phthalate, malathion, trisodium nitrilotriacetic acid, phenol, and polychlorinated biphenyl (Capacitor 21). A closed system devoid of standing air space greatly reduced volatility as a test variable. Mechanical homogenization proved highly effective in suspending hydrophobic compounds in influent water. Continuous agitation in the test chamber and regulation of detention time further precluded the need for carrier solvents. Test results indicated good reproducibility of exposure concentrations. The most toxic compounds included Capacitor 21, chlorobenzene, 2,4-dichlorophenol, and phenol. Chlorobenzene at 90 micrograms/l produced complete lethality of trout eggs. The three other compounds gave log profit LC50's of 2 to 70 micrograms/l when trout stages were exposed in hard water, and LC1's were 0.3, 1.0, and 1.7 micrograms/l for phenol, Capacitor 21, and 2,4-dichlorophenol. Chloroform also was highly toxic to trout stages and LC1's ranged from 4.9 to 6.2 micrograms/l. When bass and goldfish stages were exposed to chlorobenzene, LC1's ranged from 8 to 33 micrograms/l. Compared to other species, trout developmental stages generally exhibited the greatest sensitivity. The LC1 values determined in embryo-larval tests compared closely with maximum acceptable toxicant concentrations developed in life-cycle studies. Most compounds produced appreciable frequencies of teratic larvae.