The "radiomimetic" chemicals nitrogen mustard (HN2) and triethylene melamine (TEM) induce cataracts in female RF mice similar to those caused by ionizing radiation.1 Studies2 on 4-(p-dimethylaminostyryl) quinoline (4M20) suggested the possibility that the "radiomimetic" effects of this drug might also include induction of lens opacities. This paper reports the observation that 4M20 is highly cataractogenic to the mouse lens. Methods The 4M20·HCl form of the compound, prepared at pH 1.5 as a 20% solution in distilled water, was administered intravenously into the tail of ten-week-old female RF/Up mice in doses of 0.075, 0.095, and 0.10 mg/kg. The LD50/30-day dose level is reported as 0.11 mg/kg for mice of this strain.2 Control mice were injected intravenously with 0.2 ml HCl at pH 1.5. The mice were housed in groups of ten per cage and allowed free access to Purina Laboratory Chow and drinking water.