Eighty children, between 1-12 years, suffering from recurrent respiratory infections were admitted to a multicentre study and treated with thymopentin, an immunomodulating compound that represents the active site of the natural thymic hormone thymopoietin. Thymopentin efficacy, measured as reduction in the number of infective episodes, and tolerability were assessed and, at the end of the study a global evaluation was made by each investigator. Moreover, the following factors were recorded: clinical course, duration of symptoms/signs, frequency of administration of antipyretic, antibiotic, anti-inflammatory and mucolytic therapy, school attendance and hospitalization. Thymopentin treatment resulted in a statistically significant decrease of infective recurrences. The use of symptomatic and antibiotic drugs was also reduced. Side effects were few and mild. The investigators' overall evaluation of thymopentin's efficacy and tolerability was favourable. In conclusion, thymopentin, administered subcutaneous for 5 weeks in winter, may be useful in the treatment of children with recurrent infections of the respiratory tract.