Chlorpromazine inhibited the hatching of eggs of the parasitic nematod
e Haemonchus contortus and the free-living nematode Caenorhabditis ele
gans. In both species, hatching occurred st a concentration of 100 mu
g/ml but was almost totally blocked at 400 mu g/ml. In the case of C.
elegans, the effect was shown to be reversible by removal of chlorprom
azine after exposure of the eggs to the drug for 1 hr. Caenorhabditis
elegans larvae that hatched in a chlorpromazine concentration of 100 m
u g/ml were killed, but those that hatched in a concentration of 6.25
mu g/ml were not. Taken together with data published by others, these
observations indicate that the first-stage larva of C. elegans is less
sensitive to chlorpromazine than is the adult worm.