The relationship of left-handedness to allergic disorders and stuttering, using epidemiological data of two French samples, is reported from L'Institut National de la Sante et de la Recherche Medicale, Villejuif, France. A higher frequency of stuttering, but not of allergic disorders, occured in left-handers. Extreme right-handedness was significantly associated with a lower frequency of allergic disorders. The Geschwind-Galaburda theory of cerebral dominance was not supported by these findings. Any significant association of allergic disorders with handedness disappeared after the exclusion of the extreme right-handers. On the contrary, stuttering was associated with left-handedness even after exclusion of extreme handedness. 
COMMENT The Geschwind-Galaburda theory of cerebral dominance invokes in utero testosterone-induced-immune disorders and left-handedness by effects on the thymus and the brain. Their clinical observations showed a higher frequency of inmune diseases, migraine, and developmental learning disorders in left-handed individuals and their families.