Cigarette smoke condensate (CSC) was fractionated for bioassay to determine possible tumorigenic activity on mouse skin. Two fractions which previously had shown activity were further separated. A weak-acid fraction (F 8) was separated into three subfractions. A polynuclear aromatic hydrocarboncontaining fraction (F 20) was divided into two fractions by gel permeation chromatography. The polynuclear aromatic hydrocarbons, the suspected active materials in F 20, were successfully concentrated into a fraction (F 55) representing only 0.05 % of CSC. These materials are currently undergoing bioassay.