Lycopene is one of the major carotenoids and is found almost exclusively in tomatoes and tomato products. Since tomato consumption is associated with decreased risk of prostate cancer, characterizing the effects of lycopene on cell growth or survival, cell cycle progression, and apoptosis in LCNaP human prostate cancer cells might elucidate the mechanisms of actions of lycopene. To discover the possible anti-cancer mechanism of lycopene, water-soluble lycopene was used, and cell cycle arrest and apoptosis were measured. Placebo formulation at each lycopene dose at 0.1, 1, and 5 microM was used as a control. After 6, 24, and 48 hours of incubation, cells were harvested and measured for cell viability. Lycopene at 1 microM inhibited cell growth by 31%, compared with its placebo formulation after a 48-hour incubation. Lycopene at 5 microM increased the number of cells in the G(2)/M phase of the cell cycle from 13% to 28% and decreased S-phase cells from 45% to 29%, while no shifts in cell cycle were detected in placebo-treated groups. Apoptosis was observed at the 5 microM lycopene formulation at the late stages during the 24- and 48-hour treatments. Lycopene, therefore, deserves further study as a potential chemopreventive/chemotherapeutic agent.