1. 1. Respiratory activity and total lipid content were measured on whole blood samples obtained from 4-week-old sexually immature Japanese quail of both sexes. 2. 2. For the combined group of males and females, the mean oxygen consumption of the blood of control quail was 164 μl/ml per hr, stilboestrol-treated birds 118 and testosterone-treated birds 174. 3. 3. Blood lipid levels were 1·89 g/100 ml in control, 1·42 in stilboestrol-treated and 1·92 in testosterone-treated quail. 4. 4. The addition of glucose to the blood samples did not alter the respiratory activity.