The effects of pH, temperature, aeration rate, initial sugar and ammonium sulphate concentrations, and activator (cotton seed oil and Tween 80) addition on the growth and carotenoids production properties of Rhodotorula mucilaginosa, a soil yeast was investigated in a batch system. Optimum pH and temperature for total carotenoids production were determined as 7.0 and 30 degrees C, respectively. Total carotenoids concentration and carotenoids production yield were significantly increased with increasing aeration rate up to 2.4 vvm. An initial ammonium sulphate concentration of 2 g 1(-1) gave the maximum carotenoids production. Only cotton seed oil enhanced the carotenoid productivity at a lower glucose concentration. Glucose, molasses sucrose and whey lactose sugars were chosen as the carbon sources in this study. In general, the increase in sugar concentration increased the growth of yeast and total carotenoids production. The highest carotenoid concentration (89.0 mg total carotenoids per liter of fermentation broth) was obtained when 20 g 1(-1) molasses sucrose was used as the carbon source while the highest product yield (35.0 mg total carotenoids per gram of dry cells) was achieved when 13.2 g 1(-1) whey lactose was the carbon source in the broth. (c) 2005 Elsevier Ltd. All rights reserved.