In 1985, algal biomass, primary productivity (incorporation of 14C, acidified water sample), excretion of organic matter (exudation), and bacterial secondary productivity were followed off the SW coast of Finland, in the nothern Baltic Sea. Molecular size fractionation of the dissolved (net) excreted organic carbon pool (EOC,) was carried out by gel filtration. During the phytoplankton growth season the mean algal standing stock was 0.54 g C m-', and picoalgae ( 10 000 daltons) were also observed. On the basis of the size of the excreted compounds, exudation probably took place via mediated transport across the algal cell membrane, rather than via passive leakage from the cell.