The authors tested the effect of temperature on the survival of rainb ow trout iSalmo gairdneri ) and brown trout (Salmo trutta ) egg s. In both these species, a rise in temperature reduced the fertile life of the eggs. In the rainbow trout, temperature apparently only increased metabolism because the eggs retained the same fertilizability for the same number of degrees/days, whether the temperature was 10 or 20 degree C. In the brown trout, a 15 degree C temperature was rapidly lethal for the eggs; fertilizability loss was quicke and higher at 15 degree C that at 10 degree C for the same number of degrees/days. The effects of temperature on the gamete survival of both these species were also tested after the incorporation of increasing doses of lindane and pyralene 3010 (P CB) in the diluter. In the rainbow trout at 10 degree C the lindane, applied for 20 and 40 min, at doses of 0.25, 2.5 and 25 ppm, was not toxic for the eggs; on the other hand, fertilizability decreased sign ificantly (P < 0.01) at 20 degree F.