1. Twenty-two schizophrenic patients and 22 preclinical medical students were skin tested with a battery of allergens, histamine and cantharides, to test experimentally the hypothesis that psychosis involves diminished ability to react allergically.2. The patient group showed no diminished ability to react allergically when compared with controls, but did have consistently smaller wheal response to histamine.3. It is suggested that while neither hypoergic nor hyporeactive in the skin, the schizophrenic patient may differ from the normal with respect to certain links in the allergic process, and may so differ without of necessity clinically manifesting this.4. Alteration in central nervous system function in schizophrenia—possibly diencephalic or reticular—may account for the differences in histamine response and the reported differences in autonomic responsivity, in ability contemporaneously to develop sensitization and to respond to antigen with high titre of antibodies.Abstract Teaser