Glucose at 3 g l(-1) markedly accelerated growth of Synechococcus sp. PCC 7002. The net photosynthesis rate was 263 mumol O-2 (mg Chl a h)(-1) for mixotrophic culture and 146 mumol O-2 (mg Chl a h)(-1) for photoautotrophic culture. Additing 1 g NaHCO3 l(-1) to the glucose-supplemented culture enhanced the photosynthetic rate by 18%, and the total carbon consumption rate was raised to 2.5 mg l(-1) (mg chl a h)(-1) from a previously negative value. An interaction between organic and inorganic carbon metabolism was established.