The study is ongoing, and samples from patients receiving fentanyl as a continuous I.V. infusion or a transdermal system (patch) have been collected on 15 patients. We have analyzed one set of patient samples collected following drug delivery via a patch using our gas chromatographic procedure for the quantitation of fentanyl. We are also in process of validating the RIA procedure, that is being employed at another laboratory, with ours before proceeding with sample analysis.