Abstract: OBJECTIVE To discuss the possibility of applying human cell line activation test in vitro to skin sensitization test for hair dyes. Compared with skin sensitization test in vivo, it was evaluated that advantages and disadvantages to apply human cell line activation test in vitro to skin sensitization test with hair dyes. METHODS In terms of OECD guideline 442E, 4 different shampoos were tested in human cell line activation test with human leukemia THP-1 cells by flow cytometer. And this result was compared with result from Buehler test in vivo. RESULTS From human cell line activation test in vitro, it showed that #2, #3 and #4 hair dyes got the same negative results, from which showed all the CD54RFI were < 200 and CD86RFI were < 150, compared with the traditional skin sensitization test in vivo. However, #1 hair dye got the positive result from human cell line activation test, which were different from the result in Buehler test in vivo. CONCLUSION It has advantages of short test cycle, simple test method and objective evaluation in human cell line activation test in vitro for skin sensitization test with hair dyes, and disadvantages of reflecting part of process of skin sensitization, existing the possibility of false positive.