The effects resulting from the administration of therapeutic doses (1,200 mg/day for 8 days) of miocamycin, a novel macrolid derived from midecamycin, on theophylline elimination kinetic were investigated on 25 patients affected with chronic obstructive pathology on the respiratory tract. The curves of theophylline clearance, recorded before and after the treatment with miocamycin have shown to be perfectly overlapping (trend analysis). The assumption that the capacity of slackening the theophylline pharmacokinetic would be tightly bound to the particular structure of some macrolids appears to be fully confirmed by the results of the present investigation. When miocamycin is administered in combination with theophylline, the monitoring precautions of plasma levels of the latter are practically of no use.