The goal of this study was to examine the in vitro antiproliferative activity of crude methanol extracts of three traditional Korean medicinal plants: Achyranthes fauriei, Epimedium koreanum Nakai and Scutellaria baicalensis before and after heat processing. The extracts were screened for antitumoral potential by means of an MTT assay on four human cancer cell lines: lung cancer cells (Lu1), colon cancer cells (Col2), oral epidermoid carcinomas (KB) and hormone-dependent prostate cancer cells (LNCaP). None of the extracts showed significant activity against any of the cancer cell lines. However, after treatment with steam, the processed Achyranthes fauriei extract exhibited a slight, but enhanced cytotoxic activity against all four of the cancer cell lines. The processed Scutellaria baicalensis extract exerted a potent cytotoxic activity against the Lu1 cell line in a specific manner with an IC(50) value of 14.3 microg/mL. The Epimedium koreanum extract showed no cytotoxic effects against any of the cancer cell lines with or without heat processing. These results suggest that the heat processing of medicinal plants represents a possible route to the development of antitumor agents.