External ATP in concentrations of 10(-6)--10(-3) M is shown to stimulate the label incorporation from intracellular labeled pool of 14C-leucine into proteins of mollusc nervous tissue. The maximum effect (by 45% higher than in control) is observed at the 10(-5) ATP concentration. In solutions with high concentration of bivalent ions, ATP action increases by 10--15%. Being incubated for an hour in physiological solutions without energic substrates nervous tissue loses 30--50% of labeled amino acids. Outwashing of 14C-leucine depends only a little on the bivalent ion concentration in the external solution and on the presence of helating agents. Addition of 10(-4) M ATP into the solution, completely inhibits the washing of amino acids out of tissue. At low bivalent ion concentrations 14C-leucine incorporation into nervous tissue in the presence of ATP changes inversely to the ATP concentration: low ATP concentrations (10(-5)--10(-6) M) activate label incorporation by 60--40%, whereas high concentrations lead to the corresponding inhibition. This inhibition is due to helating action of ATP.