Abstract. The aim of the study was to study the parameters of acute toxicity, gender effects, and activity of apoptosis modulator proteins bcl-2, caspase-3, and hsp70 in albino rat brain neurons in response to administration of silver, bismuth, gadolinium nanoparticles-containing nanocomposites. Parameters of acute toxicity of nanobiocomposites were determined by intragastric administration. Subacute toxicity was studied by intragastric administration of nanocomposites for 9 days at a rate of 500 µg/kg body weight. Immunohistochemical method was used for assessment of modulators of apoptosis of bcl-2 and caspase-3 in albino rat brain neurons and the activity of heat shock proteins. All nanobiocomposites belong to a low-hazard class of substances on the parameters of acute toxicity. At the same time, in a subacute experiment, despite the same matrix, the response of the organism was specific depending on the metal nanoparticles encapsulated in the matrix. Administration of silver nanocomposites caused proapoptotic effect in brain cells. Bismuth and gadolinium nanocomposites did not stimulate of programmed cell death in brain.