We studied 13 children and adolescents during diabetic ketoacidosis; the duration of diabetes ranged from 1.4 to 6.0 years. A group of 13 diabetic sex, age and duration of disease-matched children served as control. Patients in ketoacidosis showed important abnormalities of T subset percentages (OKT3: 63.4 +/- 1.87% vs 72.1 +/- 3.4; p less than 0.001. OKT4: 37.18 +/- 1.85% vs 44.6 +/- 3.9; p less than 0.01. OKT8: 28.5 +/- 6.51% vs 28.1 +/- 1.9; p less than 0.04) and impaired neutrophil chemotaxis (53.10 +/- 3.3 vs 88.1 +/- 7.2; p less than 0.001). The patients showed normal levels of all classes of immunoglobulins. No correlation was observed between these abnormalities and the degree of ketoacidosis or glycaemia. When the patients were re-evaluated out of ketoacidosis, the values of the immunological parameters were normal and similar to those of the control group.