The process of conidiation in Neurospora crassa consists of a series of distinct developmental stages culminating in the formation of multinucleate asexual spores called macroconidia. Immunoblotting techniques were used to study the timing of synthesis and cellular localization of CON10 and CON13, the products of two genes that are expressed during conidiation but not during mycelial growth. Both proteins first appear about 8 hr into conidiation; CON10 disappears between 2 and 4 hr after germination. Within conidiating cultures, CON10 and CON13 proteins are localized in conidiophores, with little or no protein present in the underlying mycelium. Immunofluorescence analyses show that CON10 is evenly distributed throughout the cytoplasm of macroconidia. Synthesis of CON10 and CON13 occurs at a time when their specifying mRNAs first appear (Hager and Yanofsky, Gene 96, 153-159, 1990; Sachs and Yanofsky, Dev. Biol 148, 117-128, 1991), suggesting that regulation of synthesis is predominantly transcriptional.