The lipid, fatty acid, glucan, protein, and chlorophyll contents of nutrient-starved and nutrient-stressed cells ofCyclotella meneghinianaKütz. were investigated in batch and semicontinuous culture experiments, respectively. In batch culture experiments, cells were removed from nutrient-replete media, resuspended in silicon-, nitrogen-, or phosphorus-deficient media according to a 2 × 3 factorial design in fractional replication, and analyzed 3 and 9 days after transfer to treatment media. Silicon starvation caused a significant increase (300%) in cell protein content. In semicontinuous culture experiments, cells were grown in media with silicon, nitrogen, or phosphorus at concentrations lower than necessary for maximum rates of growth. Within each nutrient experiment, dilution rates of 0.10, 0.25, and 0.50∙day−1produced three distinct rates of nutrient supply per cell. Cell lipid : glucan ratios significantly decreased (50%) with increasing silicon supply rate. Cell lipid, glucan, and protein significantly increased (300%) with increasing nitrogen supply rate. Cell lipid and glucan significantly increased (300 and 400%, respectively) with increasing phosphorus supply rate. Fatty acids of extracted lipids generally possessed carbon chain lengths of 14 to 24. However, carbon chain lengths of fatty acids from silicon-stressed cells ranged from less than 14 to 18. No distinct differences in fatty acid composition were observed among supply rates within silicon- and nitrogen-stressed culture