The authors present their experiences with doxycycline in the treatmend of 54 patients, 16 of them with different infectious diseases, 18 Staphylococcus aureus carriers and 20 Streptococcus beta haemolyticus carriers. The drug was given in a single oral dose for several days according to the degree of severity of the disease; tolerance to the drug was good. Doxycycline was very effective in the treatment of Staphylococcus aureus and Streptococcus beta haemolyticus infections.