A young Caucasian male, otherwise healthy, had had generalized anhidrosis since early childhood. During heat stress tests (40 degrees C, 40% relative humidity), he was found to be heat intolerant since sweat was not apparent. His reaction to muscarinic stimulation of sweat glands was 10% of normal. On biopsy, the sweat glands were morphologically intact, and function of his cardiovascular autonomic responses was normal. The patient's mother reported reduced sweating and her response to muscarinic stimulation was 50% of normal, but his father and both sisters sweated normally. The data suggest a post-ganglionic defect, which may be genetic. To our knowledge this is the first reported case of familial generalized anhidrosis without anatomopathological lesions affecting sweat glands.