Arterial injury-induced vascular smooth muscle cell (VSMC) proliferation in intima is the important etiologic factor in vascular proliferative disorders such as atherosclerosis, hypertension and restenosis after balloon angioplasty. Butyrate, a naturally occurring short chain fatty acid, is produced by bacterial fermentation of dietary fiber and by mammary glands of certain mammals. Studies have shown that butyrate at millimolar concentrations, which are physiological, induces growth arrest, differentiation and apoptosis. We examined the effect of physiological concentrations of butyrate on rat VSMC proliferation and proliferation-induced PCNA expression to determine anti-atherogenic potential of butyrate. Butyrate concentrations, closer to physiological range, exhibited antiproliferative effects on both serum-induced proliferation of serum-starved quiescent VSMCs and actively proliferating non-confluent VSMCs. Treatment of serum-starved quiescent VSMCs with 1-8 mmol/l concentration of butyrate caused a concentration-dependent decrease in serum-induced VSMC proliferation and cell proliferation-associated increase in total cellular proteins and RNA levels. Similarly, exposure of actively growing VSMCs to 5 mmol/l butyrate resulted in the inhibition of cell proliferation and proliferation-induced increase in cellular proteins and RNA levels. Furthermore, cellular morphology was significantly altered. Analysis of cell cycle regulatory proteins indicated that levels of PCNA, an excellent marker for cell proliferation, was significantly altered by butyrate both in actively proliferating and serum-induced quiescent VSMCs. These observations suggest that butyrate exhibits potential antiatherogenic capability by inhibiting VSMC proliferation and proliferation-associated increase in PCNA expression and thus merits further investigations regarding therapeutic significance of butyrate in vascular proliferative disorders.