Urine analysis gives an insight into the excretion of the administered drug which is related to its reactivity and toxicity. In this work, the capability of inductively coupled plasma mass spectrometry (ICP-MS) to measure ultratrace metal levels was utilized for rapid assaying of gallium originating from the novel gallium anticancer drug, tris(8-quinolinolato)gallium(III) (GaQ(3)), in human urine. Sample dilution with 1% (v/v) HNO(3) as the only required pre-treatment was shown to prevent contamination of the sample introduction system and to reduce polyatomic interferences from sample components. The origin of the blank signal at masses of gallium isotopes, 71 and 69, was investigated using high-resolution ICP-MS and attributed, respectively, to the formation of (36)Ar(35)Cl(+) and (40)Ar(31)P(+) ions and, tentatively, to a triplet of doubly charged ions of Ba, La, and Ce. The accuracy and precision performance was tested by evaluating a set of parameters for analytical method validation. The developed assay has been applied for the determination of gallium in urine samples spiked with GaQ(3). The achieved recoveries (95-102%) and quantification limit of 0.2 μg L(-1) emphasize the practical applicability of the presented analytical approach to monitor renal elimination of GaQ(3) at all dose levels in clinical trials that are currently in progress.