A kinetic study of the initial step of the nitrosation of synephrine, N-acetylsynephrine and ephedrine by sodium nitrite has been carried out in acid medium at 31 0 K and ionic strength 0.36 mol dm-3. In order to simplify the reaction, [nitrite] > [amine] has been used. The absorbance changes at 300 nm (synephrine and N-acetylsynephrine) and at 332/323 nm (ephedrine). were measured and then analysed according to the initial rate procedure. The results are interpreted on the basis of a simultaneous nitrosation of the amine and phenolic groups in synephrine. Unlike the early reports the global constants for N-nitrosation (0.142 dm6 mol-2 s-1) and C-nitrosation (3.6 x 10(-4) dm3 mol-1 s-1) obtained at pH 3 in unbuffered medium indicate that the rate of nitrosation of the amino group is one order of magnitude larger than that for the phenolic group.