Peripheral T lymphocyte subsets were investigated, using monoclonal antibodies, in 14 patients with acute diabetes of duration less than 1 month (before insulin treatment) and after prolonged strict blood glucose control, and also in 40 healthy volunteers. At the time of diagnosis, the percentage total T cells was decreased (67.6 +/- 8.4 versus 72.8 +/- 6.6%), but T4 'helper' cells and T8 'suppressor/cytotoxic' cells were in the normal range. The T4/T8 ratio was not significantly higher than in the control group and B-cell percentages were increased (IgS: 18.3 +/- 7.1 versus 12.4 +/- 4.9%). The second T cell enumeration, performed after sustained normoglycaemia, showed a normal total T cell percentage and a decrease in the T4/T8 ratio depending on a decrease of T4 cells (38.3 +/- 12.8 versus 49.3 +/- 13.4), without any change of T8 lymphocytes; B cells remained elevated. These results suggest that insulin deficiency/metabolic derangement was responsible for an imbalance of circulating lymphocytes and underlines the importance of metabolic control in the assessment of such immunological parameters.