Abstract 1. 1. Normal serum glutamic oxalacetic transminase (SGOT) and alkaline phosphatase (AP) levels were determined in albino mice. 2. 2. The SGOT range of activity for 330 apparently healthy adult mice was 30–380 units/ml serum, with a mean of 148 and standard error of 3·3. 3. 3. For AP, the range of activity for 306 apparently normal adult mice was 10–210 mU/ml (international milliunits/ml), with a mean of 67 and a standard error of 1·7. 4. 4. The means and range for the normal activity of both enzymes in mouse serum were considerably higher than those obtained for human serum analyzed using the same analytical procedures.