Immunological disorders seem to be of considerable relevance to the pathogenesis of Crohn's disease (CD). T-cells play a central role in immunoregulation. The T-cell subpopulations of 70 patients with CD were compared to those of age- and sex-matched healthy controls. The suppressor-inducer subpopulations were found to be reduced in CD patients irrespective of wether they were taking steroids or not. In contrast to other subpopulations suppressor-inducer cells remained unchanged during follow-up. The results point to a disturbance in the regulation of suppressor T-cells in patients with Crohn's disease.