This study presents results on the availability of various organic P compounds for bacteria from mesotrophic Lake Constance. The rates of hydrolysis of all tested compounds added to the analyzed lake water samples did not correlate with assimilation of liberated inorganic P. beta -glycerophosphate and AMP were the most efficiently hydrolysed by bacterial phosphohydrolytic enzymes. The highest specific P uptake was found in water samples supplemented with nucleotides. The fastest increase in bacterial numbers was observed in water samples enriched with DNA, RNA, ATP and phytin. Analysis of discrepancies between rates of hydrolysis, specific P uptake and bacterial growth rates in samples enriched with various organic P compounds suggested that bacterial phosphatases participated substantially in processes of dissolved organic carbon (DOC) compound decomposition in lake water, whereas 5'-nucleotidase was mainly responsible for bacterial P demand.