195Pt and 15N nuclear magnetic resonance (NMR) was used to study the chemical equilibria of cisplatin in water and plasma ultrafiltrate (PUF). Cisplatin was found to be stable for at least 2, but no longer than 5 months in a reconstituted clinical formulation, as determined by 195Pt NMR. In aqueous solution, the cis-PtCl2(NH3)2 195Pt and 15N NMR signal intensities decreased with time and the formation of [PtCl(H2O)(NH3)2]+ at PH values of 3.0, 6.5, 7.5 and 9.5 was observed within 24 h of sample preparation. In addition, [Pt(H2O)2(NH3)2]++ was observed at pH 3.0, and [PtCl(OH)(NH3)2] and [Pt(OH)2(NH3)2] were observed at pHs 7.5 and 9.5. During incubation of PUF with cisplatin for 35 h, 15N NMR signals for at least eight cisplatin derivatives appeared at different times, whereas only four were observed by 195Pt NMR. With our NMR protocols, the detection limit for quantifiable cisplatin derivatives is estimated at 500 microM using 195Pt NMR and < or = 200 microM using 15N NMR. In addition to providing useful information about the chemical stability of cisplatin and derivatives formed in aqueous solution, these magnetic resonance techniques, particularly 15N NMR, can provide useful information about the metabolism of cisplatin in biological regimes.