The potential use of systemic gadolinium chloride pretreatment of rats as a tool to inhibit pulmonary macrophage function was studied by measurement of its effect on phagocytosis and nitroblue tetrazolium reduction by alveolar and interstitial macrophages. Gadolinium chloride solution was administered through the tail vein 48 h before the animals were killed. At 10 mg/kg, a dose which is generally used to inhibit Kupffer cell function, no effect on pulmonary macrophages was observed. Neither did a higher dose, 20 mg/kg, affect pulmonary macrophage function. It is concluded that gadolinium chloride pretreatment does not affect alveolar and interstitial macrophages upon systemic administration at doses and time after administration that generally depress Kupffer cell functioning.