The zygomycete fungus Blakeslea trispora is used commercially as natural source of beta-carotene. beta-Carotene production is strongly induced during mating of two strains of the opposite sex and results in the production of the pheromone trisporic acid, which in turn stimulates enhanced beta-carotene biosynthesis. beta-Carotene production is due to the enzymatic activity of phytoene synthase, lycopene cyclase and phytoene dehydrogenase. The corresponding genes, carRA and carB, were isolated from a cosmid library generated from B. trispora strain ATCC14272. The steady state level of carB and carRA mRNA transcripts under different mating conditions was monitored by both northern blot analysis and quantitative real-time PCR. The steady state levels of carRA and carB mRNA of non-mated and mated B. trispora were quantified relative to transcript levels of the translation elongation factor 1alpha-encoding tef1 gene, since tef1 is transcribed independently of mating. Transcription levels of both carB and carRA were strongly induced only under mating conditions. These data suggest that beta-carotene production in B. trispora is due to increased transcription of the biosynthesis genes carB and carRA.