The expression of mRNAs coding for 1-deoxyxylulose-5-phosphate synthase (DXS) and phytoene synthase (PSY) were studied in Dunaliella salina grown under nitrogen-sufficient (NS) and nitrogen-limited (NL) conditions. Under NS conditions growth was 2.5 times higher than under NL conditions. No differences were found in chlorophyll a content per cell, and total carotenoid content per cell was 5.33 pg 1(-1) for the NS treatment and 7.76 pg 1(-1) for the NL. DXS transcripts exhibited diminished expression under NL conditions, peaking at day 15 of cultivation in both treatments. Simultaneously, PSY transcripts exhibited constant expression under both conditions. These results suggest that these genes play an important role in the balance of photosynthetic pigments during pigment accumulation.