For research into sources of infection it is very important to distinguish one strain of an infective agent from other strains of the same species by characteristics peculiar to it alone. The relatively unvarying properties which are used to differentiate species (e.g. typical fermentation and assimilation patterns) are not suitable for this purpose. Different authors have utilized for this purpose either morphological features or enzymatic and also, most recently, resistance characteristics vis-à-vis certain fungicidal agents. The so-called Resistogram method of Warnock and a combination test set by Odds have proved especially useful. Like these 2 authors, we, too, addressed ourselves once again to the question whether vaginal reinfections are frequently due to associated intestinal colonization by Candida albicans and infection of the vagina from this reservoir. Initial studies by Warnock seemed to refute this hypothesis. However, our own data and later studies by Warnock did confirm the above assumption.