The effects of tritoqualine (TRQ) on established cell lines of fibroblasts, Balb/3T3 and 3T6, were investigated with respect to growth and collagen secretion. TRQ suppressed growth rate in the log phase and inhibited collagen secretion in the stationary phase of both cell lines. However, TRQ was not cytotoxic because of lack of influence on cell maintenance in the stationary phase. These effects of TRQ are thought to be very important as a mechanism of inhibitory action against liver fibrosis in chronic liver injury in rats.