Resorbable polymer of hydroxybutyric acid labeled with ¹⁴C was used to prepare microparticles that were then injected to laboratory animals via the tail vein, without causing any adverse effects on growth and development of the animals or altering the macroscopic and microscopic structure of the tissues of internal organs. Examination of the distribution of microparticles among the internal organs and the dynamics of accumulation of carbon-containing polymer degradation products in internal organs showed that the main targets for microparticles were tissues of the liver, kidneys, and spleen. The most rapid degradation of the polymer scaffold of microparticles occurred in the spleen and liver. The presence of high-molecular-weight polymer scaffold registered in internal organs suggested that microparticles remained undegraded and that PHB microparticles could function in vivo for extended periods of time (up to 12 weeks).