NPG(null pigmentation) mutant named for the loss of pigmentation capacity throughout the whole life cycle showed normal tip growth but retarded hyphal branching and differentiation. The retardation of sexual and asexual differentiations seemed to be partially due to retarded hyphal branching, but mainly due to reduced thallic density in spite of normal thallic size. This retardation of thallic growth significantly affect the pattern of development according to the allelic type of velA gene. Asexual development proceeded prior to sexual one in NPG mutant with velA1 allele even though the process was much delayed. In NPG mutant with velA+ allele, however, asexual development was almost completely blocked and only sexual one proceeded. When NPG mutant with velA+ allele was induced to differentiate after being grown sufficiently at uninduced condition or at the heterokaryotic state with velA1 mutant, it developed asexual spores normally, indicating that velA gene might play as negative regulator of asexual development before the thallus grew to a certain mass.