This study examined the effect of different salt concentrations (0.05-3 M of NaCl) on the kinetics of growth, total carotenoids and beta-carotene (all-trans and 9-cis) accumulated in Dunaliella tertiolecta DCCBC26, a microalgae strain isolated from the Urmia hypersaline lake, northwest of Iran. Results indicated that the highest amount of carotenoids detected (11.73 mg/l) was in the salinity of 0.5 M NaCl during the stationary growth phase. The percentage of the all-trans and 9-cis-beta-carotene in the exponential phase were 92% and 32% in salinities of 3 M and 0.5 M, respectively. However, only 23% of the beta-carotene was detected in the stationary growth phase of the microalgae in 0.5 M salinity and was 9-cis isomer. (c) 2005 Elsevier Ltd. All rights reserved.