Introduction
Reports that serum from schizophrenic subjects has significantly greater "amine oxidase" activity than that from normals4, 13,31 stimulated many workers to explore this finding as a possible diagnostic tool or etiological clue. As so frequently the case, both confirmatory1,2,3,5,12,32,43 and contradictory6,7,16,17,28 findings soon appeared and some confirming authors found the overlap of populations was so great as to exclude any possible diagnostic application.2,46These studies were mostly carried out on small experimental populations, often differing in such critical factors as age, nutritional state, activity level, concomitant medical treatments, etc. In the present study this problem has been reexamined with matched populations under a variety of conditions. Four of the more commonly used procedures for "serum oxidase" activity have been compared; several factors, thought to influence the test results, have been studied; and various theories on the physiological significance of "serum oxi