In cyanobacteria, the elevation of unsaturated fatty acid levels in membrane lipids has been shown to play a major role in the response to temperature change. The cyanobacterium Spirulina platensis strain C1 contains three desaturases - Delta(9), Delta(12) and Delta(6) desaturases - which are encoded by desC, desA and desD, respectively. In light of the above, a study was conducted of the regulation of desaturase gene expression in response to temperature change in S. platensis strain Cl. The two lipid membranes, thylakoid and plasma, were separated, while the expressions of the desaturase genes to the downward shift of growth temperature were studied in the translation level by Western blot analysis. The results revealed that the expression of Delta(9) desaturase is independent of temperature. In the case of Delta(12) desaturase, two forms of the enzyme were found, at 45 and 40 kDa. In terms of correlation with the results in the transcription level, it is more likely that the 45 kDa-Delta(12) desaturase and the 40 kDa-Delta(12) desaturase are translated from 1.7 kb and 1.5 kb mRNA, respectively. Taken together, the results indicate that the expression of the 40 kDa-Delta(12) desaturase is temperature independent, whereas, the 45 kDa protein form demonstrates a response to the immediate temperature reduction. Furthermore, the activity of Delta(6) desaturase in the two lipid membranes is possibly regulated by temperature reduction. However, alteration in the level of gamma-linolenic acid, the product synthesized by Delta(6) desaturase, was observed in the plasma membrane prior to the thylakoid membrane.