Although crude coal tar is a mixture of approximately 10,000 components, few attempts have been made to assess the pharmacological activity of individual components of purified tar products or of different coal tars themselves. The hairless mouse epidermal DNA synthesis suppression assay, which has been shown to be useful for predicting the antiproliferative activity of topical agents, has recently been used to assess the activity of crude coal tar, coal tar extracts and tar based shampoos. Using this assay, great variation in effectiveness (0–90%) was found among tar distillate fractions, suggesting that one source of potential variation of activity in commercial coal tar products is the non‐standard composition of crude coal tar itself.