The nuclear condition of conidia and their subsequent stages of development of 2 spp. of the A spergillus glaucus series as defined by Thom and Raper, including A . echinulatus and A . repens and 2 antibiotic producing species, A. clavatus and A. fumigatus, were investigated. The conidia of A . echinulatus are multinucleate when formed, but the original nuclei entering the conidia divide freely and may possess more than 8 nuclei. In the other 3 species, conidia are formed as uninucleate cells. These become binucleate preceding germination in A. fumigatus and multinucleate in A. clavatus and A. repens. In all species hyphae become multinucleate when septa form.