Owing to their conservation and immunogenicity, heat shock proteins (hsps) represent a class of potential autoantigens. Moreover, they could be targets for gamma delta T lymphocytes, which are prominent in various immune disorders. We studied the T cell proliferative primary responses to recombinant M. bovis 65 kDa hsp (hsp65) and M. tuberculosis 70 kDa hsp (hsp70) in 31 patients with multiple sclerosis (MS), 19 patients with other neurological diseases (OND) and 19 healthy individuals. Positive responses to hsp70, but not to hsp65 were significantly more frequent in patients with MS than in patients with OND or in healthy individuals. In order to verify and refine these results and to characterize the hsp reactive T lymphocytes, we screened 147 PPD-specific long-term T cell lines (76 from 10 patients with MS and 71 from 12 healthy donors) for their proliferative response to hsp65 and hsp70. hsp70-reactive T lines were significantly more common in patients with MS than in healthy controls. The number of T lines responding to hsp65 increased in the MS group only slightly. In 19 T lymphocyte lines from patients with MS and healthy donors, a cytofluorometric analysis was performed with special attention paid to distinct T cell receptor gamma delta determinants. With one exception, in each line the population of gamma delta T cells remained a minority. We conclude that an increased T cell response to mycobacterial hsp70 may be present in patients with multiple sclerosis.