Two methods are proposed, one spectrophotometric and one spectrofluorimetric, for the determination of insulin in several pharmaceutical formulations. The methods were found to be fairly simple, sensitive and accurate, and thus suitable for this purpose. Both methods involve an extractive step with diethyl ether for the elimination of excipient interference, and subsequent direct spectrometric analysis. Spectrophotometric determinations were carried out at lambda = 276 nm; spectrofluorimetric determinations were carried out at lambda em = 306 nm with lambda exc = 277 nm.