According to current concepts, the influence of autologous platelet-rich plasma (PRP) and high molecular hyaluronates (HA) on the repair of hyaline cartilage during its inflammatory and degenerative changes has been insufficiently studied yet. The objective of the work was to evaluate the morphological changes in the structure of hyaline cartilage in experimental osteoarthritis after intra-articular injection of PRP and/or HA. Material and methods. The authors used 50 adult rats of Wistar line, weighing 250±2,2 g., distributed into five groups of 10 animals (two control and three experimental groups). An experimental gonarthosis was simulated on four groups of animals. Animals of the first experimental group received intra-articular injection of PRP, the second group – HA, the third – both PRP and HA. Results. No morphological signs of degenerative and inflammatory changes in the first control group were identified. Following osteoarthritis simulation the articular cartilage thinned to 121±20,4 microns (p<0,05) and the volume fraction of chondrocyte decreased to 1,2±0,6% (p<0,05). The authors observed an uneven coloration of collagen fibers with severe tinctorial properties disorder of the articular cartilage matrix. After the RPR introduction the authors observed tickening of the articular cartilage up to 275±18,9 micron (p<0,05) and the volume fraction of chondrocytes up to 18,4±2,0% (p<0,05). Conclusion. During osteoarthritis simulation in knee joints of experimental Wistar line rats the authors observed severe structural changes in articular hyaline cartilage including complete destruction accompanied by vascular proliferation and granulomatous inflammation.