A comparison of transketolase assay and transketolase and lactate dehydrogenase activity levels in whole blood and red cell hemolysates and in leukocytes.

1. A study was made of transketolase activity in red and white blood cells and of conditions for assay for transketolase activity and for assessment of the "TPP effect" in human and rat blood. 2. The ratio of the transketolase activity in white cells to that in red cells varied between 23 and 93. 3. Red cells or white cells can both be used for assessment of transketolase activity and the "TPP effect", but the best source for evaluation of transketolase activity and the percent change on addition of thiamin diphosphate appears to be whole blood.