Estimations of the blood amino-acid N in normal children and in those in various pathological conditions, both fasting and non-fasting, are reported. The amino-acid N has consistently been found lower in fasting bloods than in non-fasting, and the mean difference due to this influence is estimated. The blood amino-acid N for normal healthy children has been determined, and by comparison with this figure it has been shown that (1) in rheumatism and chorea with or without carditis no change is found; (2) in nephritis there is a lowering of the amino N; (3) in renal and coeliac infantilism the lowering is still more marked.