Ibuprofen has wide applications in the treatment of rheumatoid arthritis and osteoarthroses as an effective non-steroidal antiinflammatory drug. The drug is still being investigated regarding its possible ability to reduce myocardial infarct size. The more potent biphenyl propionic analogue, flurbiprofen, has recently been introduced. Both drugs are strong inhibitors of cyclooxygenase. The specific HPLC-method described requires plasma samples of 100 microliter which are deproteinized and simultaneously extracted with acetonitrile containing either of the drugs as internal standard. Aliquots of 25 microliter of this primary extract were directly injected on a mu Bondapack C18 column. For elution was used a mixture of 60% methanol and 40% 50 mM phosphate buffer adjusted to pH 4.6. The detection limit (at 214 nm) for both drugs corresponded to plasma concentrations of about 0.2 micrograms X ml-1. The applicability of the method was demonstrated in a pharmacokinetic ibuprofen experiment in an adult person.