The effect of the mucolytic agent bromhexine, 72 mg daily for one month, on albumin excretion in insulin dependent diabetes was investigated in a double-blind, randomised, cross-over, placebo-controlled study. Nine patients with normal albumin excretion [overnight albumin excretion rate 3.2 (2.1-8.8) micrograms/min.; mean (range)], six with microalbuminuria [36 (22-95) micrograms/min.] and six with macroalbuminuria [321 (201-1215) micrograms/min.] participated. Albumin excretion was similar after treatment with bromhexine and placebo in all 3 groups [normoalbuminurics 3.6 (1.7-13.5) versus 3.3 (1.9-13.2) micrograms/min.; microalbuminurics 40 (20-128) versus 37 (20-103); macroalbuminurics 396 (247-2160) versus 443 (292-2592)]. Excretion of beta 2-microglobulin and creatinine clearance were identical at the end of each treatment. Blood glucose control and blood pressure remained constant throughout the study in the 3 groups. We conclude that bromhexine 72 mg daily for 1 month had no effect on albumin excretion in IDDM patients with normal and pathological albuminuria.