The form of growth of Mucor rouxii (National Regional Research Laboratory 1894) under nitrogen is dependent on inoculum size. With a large inoculum (10(6) spores inoculated per ml), the morphology consists mainly of swollen spores with some filaments and yeastlike cells. At lower inoculum levels growth is filamentous. The morphology of this strain on incubation under nitrogen and the dependence of the form of growth on inoculum size are similar to those found previously for other strains of M. rouxii.