Cell suspension cultures of Silybum marianum L. Gaertn (Compositae) produce silymarin, a mixture of flavonolignans. In an attempt to increase cell growth and silymarin production, we exposed cell cultures to various levels of Ag+ (0.2, 0.4, 0.8, 1, and 2 mM) for different exposure times (12, 24, 48, 72, 144, and 216 h). A dramatic increase in cell growth was observed after 12 h in media supplemented with 0.2, 0.4, 0.8, and 1 mM Ag+, and the value in medium treated by 1 mM Ag+ after 72 h was 7.21 g, which was about two-fold that of the control (3.32 g). The highest silymarin production reached about 56 microg g(-1) DW, 24 h after treatment with Ag+ (0.8 mM), which was 30-fold that of the control. Silybin, isosilybin, silychristin, silydianin, and taxifolin were abundant flavonolignans. Ag+ in low concentrations is a positive elicitor for cell growth and silymarin production in cell suspension cultures of Silybum marianum.