Isolated alterations in the autonomic nervous system (ANS) have been described in obstructive sleep-apnea syndrome (OSAS), but the exact nature and degree of ANS involvement in OSAS is as yet uncharted. In the present study we evaluated some autonomic nervous functions in 13 OSAS patients using cardiopressor and pupillometric tests. Almost all showed only slight alterations of ANS function, generally in the form of a hypofunction of both sympathetic and parasympathetic branches. Pupillometry was more sensitive than cardiovascular indexes in detecting neurovegetative involvement which correlated with some respiratory indices. The data suggest that autonomic involvement in OSAS is ascribable to metabolic changes (hypoxia, hypercapnia) rather than to primary "neurogenic" alterations.