Preliminary studies on the use of high resolution 1H-NMR spectroscopy for the detection of the thiol drug penicillamine and its metabolites in human urine are described. The technique is rapid, simple and requires minimal sample pretreatment. Application of NMR to the qualitative analysis of penicillamine in urine is illustrated by penicillamine disulphide formation from penicillamine following spiking into human urine and the detection of penicillamine, penicillamine disulphide and penicillamine-cysteine disulphide (following oral administration of the drug to patients).