The antibiotic erythromycin lactobionate given intravenously acts almost exclusively on Gram-positive bacteria. Even at high plasma and tissue concentrations there is an almost total absence of side-effects. It could be considered, therefore, as first choice in the treatment of patients with infectious respiratory diseases. Most of the 40 patients admitted to the present study were elderly and all had either acute or chronic and becoming acute respiratory disease. Their clinical symptoms and levels of phlogosis improved on treatment with erythromycin lactobionate without any interruption of therapy due to side-effects and toxicity. The absence of unfavourable pharmacological interactions further enhances the usefulness of the drug. In view of the excellent response to monotherapy with erythromycin lactobionate and the few groups of resistant bacteria found in those cases when it was possible to check, it was not considered necessary to investigate any synergistic association with other antibiotics. It can be concluded, therefore, that therapy with erythromycin lactobionate in patients with infective respiratory disease is favourable and patients show excellent tolerability.