The optimal conditions (ionic strength, pH, Mg2+ and ATP concentrations) for nephelometric determination of the superprecipitation reaction of the actomyosin-like protein (AMLP) from ox brain cortex are described. At low ionic strength (0.1 M KCl, 200 micrograms of protein, pH 6.8, 37 degrees) MgATP (1 mM) first causes a fast (1--2 min) dissociation of AMLP with a decrease in the optical density (A620) at 620 nm and then a slow (15--20 min) true superprecipitation associated with a substantial rise of A620. EGTA (0.1 mM) moderately, i. e. by 20%, inhibits the reaction. The effects of glycolipids (total gangliosides and cerebrosides from ox brain) and phosphatidyl choline from chicken egg yolk on aggregation (without Mg-ATP), dissociation and superprecipitation of AMLP were examined. It was found that gangliosides (40 micrograms) and cerebrosides (2--80 micrograms) cause aggregation of AMLP; phosphatidylcholine (4--160 micrograms) has no effect on protein aggregation. Gangliosides within the concentration range of 0.8--4.0 micrograms do not cause AMLP aggregation but strongly inhibit superprecipitation of the protein, whereas phosphatidylcholine (40--80 micrograms) has practically no effect on the reaction intensity. A hypothesis on regulation by glycolipids on contractile proteins from brain presynaptic membranes under varying rest--excitation conditions is postulated.