Physiological saline, 1.5% nitric acid, 1.0% formalin and 2.0% potassium dichromate were all satisfactory for embryonation of Heterakis eggs, but recovery of worms from chickens given eggs embryonated in potassium dichromate averaged only 0.85%, as compared with recoveries averaging 54.4% for the other media. Histomonas infection was detected in 8.5% of the chickens each of which received 155 eggs embryonated in potassium dichromate, and in nearly 90% of the birds each of which received 155 eggs embryonated in one of the other media. Potassium dichromate toughened the egg shells. It is believed that many larvae failed to escape from eggs treated in this way, but that others escaped and liberated histomonads, but failed to survive long enough to be recovered at observation periods 10-63 days after feeding. Presumably, these larvae had practically depleted their energy reserves in hatching. This might account for the comparatively greater infectivity for Histomonas than for Heterakis, by eggs treated in the dichromate.