The growth and carotenoid biosynthesis of the yeast Rhodotorula glutinis was studied by cocultivation with Lactobacillus helveticus in cheese ultrafiltrate containing 3.9% and 7.1% lactose. By growing this mixed culture in a 15-L fermenter MBR AG (Switzerland) at an air flow rate of 0.5 L/L min and agitation at 220 rpm for 6 days, a total yield of carotenoids of 268 mu g/g dry cells was obtained. Carotenoids were formed almost parallel with the cell growth, and a maximum production was reached at an early stationary phase. A high-performance liquid chromatographic system (HPLC) permitting simultaneous determination of major carotenoid pigments was used. The three main pigments (torularhodin, beta-carotene, and torulene) were formed in Rhodotorula glutinis, and reached a maximum concentration as follows : 182.0, 43.9, 23.0 mu g/g dry cells.