SummaryA study was carried out in 45 patients with non-inflammatory lung disease requiring resection of lung and/or bronchial tissue to investigate the effects of bromhexine on the concentrations of erythromycin in serum and in these tissues. The patients, randomly divided into three groups, were treated for 4 days before surgery with either erythromycin alone (1 g, 12-hourly) or given simultaneously with 16 mg or with 32 mg bromhexine 12-hourly. A final dose was given 2 to 3 hours before operation on Day 4. The results showed that there was no significant difference in the changes with time in serum concentrations of erythromycin after the final dose, nor with respect to the levels of the antibiotic in lung tissue, expressed as a percentage of serum concentrations. In bronchial tissue, however, the results suggested a dual dose-dependent effect of bromhexine, the lower doses appearing to increase and the higher doses to depress the concentrations of erythromycin.