Various explanations have been proposed to account for the increased incidence of moniliasis as a result of ‘broad spectrum’ antibiotic therapy, but it is generally believed that the suppression of the bacterial flora enables fungi to proliferate without competition. The pathogenicity of Candida albicans is, in any event, associated with the numbers of cells present and we have undertaken tests in vitro in an attempt to contribute more evidence on the mechanism of their proliferation in the presence of tetracycline-treated bacterial flora. The results are presented here as a preliminary communication.