Garlic (Allium sativum) is a popular spice, a remedy for a variety of ailments and is also known for its medicinal uses as an antibiotic, antithrombotic and antineoplastic agent. Epidemiological and animal studies have shown that garlic consumption reduces the incidence of cancer e.g. in the stomach, colon, breast and cervix. The aim of this study was to investigate whether garlic extract has any influence on caspase-3 activity and gene expression and on the signal induction of apoptosis in vitro. As an assay system, the flow cytometry assay, Western blotting and cDNA microarray were applied in human colon cancer colo 205 cells. Our results indicated that garlic extract, when administered to the colo 205 cell cultures, reduced the percetange of viable cells, induced apoptosis, increased the levels of Bax, cytochrome c and caspase-3, but decreased the level of Bcl-2. The results also showed that raw extract of garlic decreased the mitochondrial membrane potential and increased the caspase-3 activity and gene expression. We conclude that crude extract of garlic can induce apoptosis in colo 205 cells through caspase -3 activity, by means of a mitochondrial-dependent mechanism.