The influence of Lindane on net phytoplankton (mainly diatoms) in samples of waters from the Antarctic was investigated for 24 hours from the introduction of ɣ HCH 0,02 and 2 ppm into the environment. Changes in intensity of 14C incorporation in the light and in rate of release of 14C by the cells in the dark during consecutive light/dark periods were measured. The effect of two different Lindane concentrations in diatoms occurred 16 hours after introduction of the compound into the environment and was independent of concentration. The effect was manifested by delayed induction of photosynthesis following the dark period and also by changes in dynamic equilibrium between carbon assimilation and dissimilation. The presence of Lindane clearly stimulated 14C incorporation in the light and also enhanced the participation of 14C incorporation in overall CO2 exchange in the dark.