RESUMO
1. Two experiments were carried out to study the effects of the mutagen ethylnitrosourea (ENU) at concentrations of 1.4 to 3 500 microgram in 0.3 ml of saline (experiment 1) and 585 to 1 170 microgram in 0.1 ml of saline (experiment 2) on hatching eggs of two breeds of fowls. Hatchability (experiment 1) and survival up to 7 d of age without food (experiment 2) were assessed. In experiment 1 the hens were fed on different diets prior to providing the hatching eggs. 2. The mutagen showed a non-linear effect upon the hatchability, higher doses being less effective than small doses. 3. In the majority of cases, female embryos were more sensitive to the effect of ENU then male. 4. The mortality after hatching was also affected by ENU; the chicks from treated eggs surviving without food better then controls.