The large inter-patient variability in cyclosporin pharmacokinetics coupled with the agent's narrow therapeutic index with adverse effects resulting from supratherapeutic levels, necessitates individualization of drug dosage and therapeutic monitoring of cyclosporin blood levels. The performance of a liquid chromatographic method for the measurement of cyclosporin was evaluated and the results obtained by this method and by a specific radioimmunoassay were correlated. The method described is sensitive, selective, reproducible and easier to perform than other chromatographic methods. It is suitable for the daily measurement of cyclosporin in batches of up to 40 samples and the results correlate well with another chromatographic method and with the specific radioimmunoassay.