The number of chondrocyte-like cells after injections of phosphate-buffered saline (PBS) (control), platelet-poor plasma (PPP)-releasate, or platelet-rich plasma (PRP)-releasate. The numbers of chondrocyte-like cells in the inner anterior and posterior anulus fibrosus (AF) and the center of the nucleus pulposus (NP) were manually counted by using light microscopy. In the anterior AF, the number of chondrocyte-like cells in the PRP group was significantly higher than those of the PBS and PPP groups (P <0.01). The injection of PRP-releasate significantly increased the number of chondrocyte-like cells in the NP compared with that of the PBS group (P <0.01). Values are shown as mean ± standard error of the mean.