Objective    To evaluate the cytotoxicity in vitro of a novel prosthetic nucleus pulposus prepared in our previous work before in vivo application.     Methods    Prosthetic nucleus pulposus made by 4 different methods were prepared to check their cytotoxicity by culturing mice fibroblast L929 cells respetively with their leaching liquor. The control group was set by culturing L929 cells with culture media. The optical density (OD) and relative growth rate (RGR) of the experimental cells were measured by MTT colorimetric method.     Results    The OD and RGR of L929 cells in the 4 material groups and the control group showed no significant difference (P0.05). The cytotoxicity of the 4 kinds of materials is at level 0-1 and they are qualified materials

according to the standard rank of cytotoxicity.     Conclusion    The neotype artificial materials show no cytotoxicity

of great potential as a substitute for nucleus pulposus.