One characteristic feature of eukaryotic cells is the organization of special functions into membranous organelles such as vesicles, mitochondria, the Golgi apparatus or nuclei. The distribution and exact positioning is an active process and is crucial for the establishment of cell polarity. For molecular analysis of the processes, filamentous fungi are ideal model organisms because hyphae are extremely polarized cells which continuously extend at their tips. In this study a novel approach was used to isolate mutants in nuclear migration and hyphal morphology. Conidia of A. nidulans, in which nuclei were stained with the green fluorescent protein (GFP) were germinated and visually analysed in a fluorescence microscope. Strains with an abnormal nuclear distribution pattern or defects in polarized growth were isolated with a micro-manipulator and transferred to agar plates to form colonies. Approximately 70 mutants with a corresponding mutant phenotype were recovered, some of which are presented in this report.