Two groups of patients were studied in order to evaluate the possible interference of miocamycin with theophylline blood levels. One group was treated with i.v. theophylline and another one was treated with slow-release theophylline. Both groups did not show any changes in theophylline blood levels. Therefore we can draw the conclusion that miocamycin, a new macrolide, is active on gram-positive and some gram-negative bacteria besides mycoplasma, legionella and chlamydia and it can be used in association with theophyllinic compounds without interaction on theophylline blood concentrations.