[Abstract] To evaluate in vitro release and transdermal behaviors of Huoxue Zhitong gel， modified Franz diffusion cell methods was applied to investigate in vitro transdermal absorption of Huoxue Zhitong gel and the content of paeonolan in receptor fluid composed of PEG400%-95% ethanol-water(1∶3∶6)were determined by HPLC. The results were processed and different equations were fitted. The release law were in accordance with Weibull equation and the fitting equation was ln[-1/(1-Q)]=-0.790 5lnt-1.701 2(r=0.980 9). In 8 hours ......