By probe sampling procedure and ESR detection, labile species have been monitored in premixed methanol-air flames doped with hydrogen sulfide and stabilized at 80 Torr. H, O, and OH as well as SO or SH species in inhibited flames have been detected. Quantitative determinations of mole fraction profiles of these species (except SH) have been achieved throughout the flames. In the absence of hydrogen sulfide, a modelling of the main reactions (OH + OH ..-->.. H/sub 2/O + O, O + OH ..-->.. H + O/sub 2/, wall destruction of OH, O, and H) occurring in the sampling probe supports the validity of the linear extrapolation to zero pressure already proposed in a previous work. The major effect of hydrogen sulfide addition is to enhance the formation of H/sub 2/ and SO/sub 2/ and to decrease the concentration of H, O, and OH species. In the burnt gases the results are compared with calculations assuming thermodynamic or partial equilibrium hypotheses. Coupled with gas chromatography for the simultaneous determination of molecular products, this method appears to be well adapted to the analysis of flame microstructure.