The effect of drugs used in the chemotherapy of tuberculosis on blood glucose, serum immunoreactive insulin and serum growth hormone, and on the half-life of tolbutamide, were studied in 16 patients with tuberculosis just before starting treatment and four weeks later using an intravenous tolbutamide test. The maximum fall of blood sugar was about 30% on both test occasions. The peak values of serum growth hormone before and after treatment (15.6+/-3.1 ng/ml and 17.3+/-2.9 ng/ml), and the maximum values of serum insulin before or after treatment (37.6+/-5.3muU/ml and 45.6+/-7.0 muU/ml) did not differ significantly from one another. The levels of serum insulin remained slightly higher in the test from 10 minutes onwards after treatment than before, but this was not associated with any particular tuberculostatic drug combination. The half-life of tolbutamide decreased by 43% and the serum concentration of tolbutamide decreased at 180 minutes by 30% and at 360 minutes by 49% after treatment in comparison with the pretreatment values in the patients receiving rifampicin in their drug combination. In patients receiving other tuberculostatic agents, no significant changes were observed.