A method is described to determine Diethylestilbestrol, Hexestrol and Dienestrol residues in bovine urine, using GC-MSD, working with the SIM system. The urine was centrifuged and the pH adjusted to 9 with 32% NaOH, then subjected to a solid phase extraction procedure using C-18 columns (Baker, spe-500). These columns were eluted with methanol, the alcohol extract was evaporated to obtain a solid residue. The derivation of the stilbene was performed with BSTFA:TMCS 99:1, incubated 15 min at 70°C. The final extracts were dissolved in acetonitrile and injected in a GC-MSD apparatus (quadrupol electronic impact). Three characteristic ions were monitored for each product studied. The detection limit achieved is 2 ppb for Diethylestilbestrol and Hexestrol and 3 ppb for Dienestrol.