Constituents in rosemary have shown a variety of pharmacological activities for cancer chemoprevention and therapy in in vitro and in vivo models. In order to further explore the chemopreventive properties of crude extracts of rosemary (Rosmarinus officinalis L), we studied its anti-proliferative property on several human cancer cell lines and its antioxidant and anti-inflammatory properties in vitro in a mouse RAW 264.7 macrophage/monocyte cell line. Our study shows that crude ethanolic rosemary extract (RO) has differential anti-proliferative effects on human leukemia and breast carcinoma cells. The 50% inhibitory concentration (IC50) was estimated at 1/700, 1/400, 1/150 and 1/500 dilutions, for the HL60, K562, MCF7 and MDA-MB-468 cells, respectively. Non-cytotoxic concentrations of RO at 1/1000 dilution minimally induced HL60 cell differentiation into granulocyte lineage at 9.5+/-2.2% compared to 2.8+/-0.8% in the untreated control (p<0.001), and did not induce HL60 cell differentiation into monocyte/macrophage lineage. The 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid (Trolox) equivalent antioxidant capacity assay showed that RO has substantial antioxidant activity with RO at 1/10 and 1/5 dilutions having 8.1 and 12.6 microM Trolox equivalents, respectively. RO at non-cytotoxic 1/2000 and 1/1000 dilutions did not affect nitric oxide (NO) production by non-stimulated RAW 264.7 cells. However, at the same dilutions RO significantly reduced NO production by lipopolysaccharide (LPS)-activated cells in a dose-dependent manner from 32.6+/-2.3 microM in the LPS-activated cells to 19.2+/-2.2 microM (p<0.01), and 7.7+/-1.2 microM (p<0.001), respectively. RT-PCR analyses showed that RAW 264.7 cells treated with 1/1000 and 1/500 dilutions for 5 h did not affect TNFalpha, IL-1beta, iNOS and COX-2 mRNA expression in these cells when compared to the untreated controls, nor did the 1/1000 dilution of RO affect TNFalpha, IL-1beta, iNOS and COX-2 mRNA expression in the LPS-activated cells. At 1/500 dilution, RO significantly reduced IL-1beta (p<0.01) and COX-2 (p<0.05) mRNA expression and non-significantly reduced TNFalpha and iNOS mRNA expression in the LPS-activated cells. In view of the chemopreventive potentials, further studies are needed to explore other biological properties of this popular spice used by many cultures in the world.