In this article a simple method for the determination of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) in biological fluids is presented, based on reversed-phase ion-pair HPLC with UV detection at 254 nm. No complicated extraction procedure is needed. The stationary phase consists of a reversed-phase C18 stainless steel column and the mobile phase of 0.005 M sodium acetate and 0.0025 M pentanesulfonic acid sodium salt (PIC-B5) as an ion-pair reagent in water (pH 6.5). DHPG is a new antiviral drug in research of the treatment of cytomegalovirus infections. As a pilot study serum and urine samples of a few patients were investigated to gain an impression of the therapeutic range of DHPG. The method is suitable for routine assay of DHPG.