AbstractCarefully polished samples of five austenitic stainless steels have been examined by reflected light microscopy and analysed, using a Link Systems model 290 KX energy‐dispersive spectrometer attached to a Cambridge Instrument Company Geoscan microprobe. At least ten different spots within apparently homogeneous areas of each sample were analysed. While the means of these analyses agree well with the published values, three of the samples have an inhomogeneous distribution of their major elements. Precipitates within the samples are mainly MnCr2O4and MnS, both with much substitution of the Mn by other elements. Other precipitates are rich in P or Nb. While such blocks are probably sufficiently homogeneous for use as bulk standards, great care should be exercised if they are to be used as microprobe standards. A small excess of silicon was found in most analyses. This is believed to be due to fluorescent excitation of silicon in the detector. Analyses of pure metals suggest that a correction of 0.12 wt % silicon should be applie