Pure W was neutron irradiated at 600 °C, 900 °C, 1000 °C, 1100 °C, and 1200 °C with a dose of ~1 dpa, and its microstructure was subsequently analyzed using transmission electron microscopy (TEM). Three types of defects were observed and analyzed in detail: (i) voids, (ii) dislocation loops with a diameter of up to 20 nm and (iii) W- Re -Os containing precipitates. The TEM study includes a detailed examination of the defect structure, e.g., determination of the size and spatial distribution of voids, precipitates and dis- location loops. Application of g-imaging shows the formation of the interstitial loops with both ½< 111 > and 100 Burgers vectors. In addition, local chemical and structural analysis revealed the formation of .-type precipitates, which are attached to the voids at 1100 °C. It was also found that voids, loops and precipitates are surrounded by a solid solution cloud enriched with Re and Os. The use of highly sensi- tive nanoscale chemical analysis allows the identification of differences in Re /Os segregation at and in the vicinity of the three defect types. A precise analysis of the chemical composition of the precipitates and clouds around the voids was achieved by a special preparation of their replicates.