Welding of stainless steels has been shown to cause localized changes in the microstructure and chemical composition which could have adverse implications for the mechanical and corrosion properties of the material. The application of several electron-optical techniques, such as transmission and scanning electron microscopies (TEM, SEM) and electron and Auger microprobe analysis (AEM), for the identification of different phases has been illustrated by the investigation of segregation effects in welded steels of AISI types 304, 304L, 316 and 31 6L. Considerable enhancement of chromium and carbon has been observed in certain well-defined zones on the parent metal and on the weld beads. Enhancement of oxygen was also observed at some of the points in these areas. The localized change in surface composition, particularly in the parent metal is attributed to the formation of the carbide M23C6 and the spinel FeCr2O4. The results were confirmed by the determination of the composition of the segregation zone, as well as the lattice parameter of some of the particles, with TEM, SEM and AEM.