Abstract The traditional technique for processing of reactor-irradiated 186W-enriched tungsten oxide (WO 3) targets involves formation of 188W-sodium tungstate solutions by target dissolution in 0.1 M NaOH. Following long irradiations (> 21 days) in the ORNL High Flux Isotope Reactor (HFIR) the 186WO 3 targets contain a NaOH-insoluble 188W-labeled black solid (approx. 30–50% of total activity) which decreases the yield and specific activity of the processed 188W (e.g. 5–6 mCi/mg 186W for a 79-day irradiation). The black material is postulated to represent a “tungsten blue” insoluble polymeric form of tungsten oxide, which we have now found to dissolve in 0.1 M NaOH containing 5% sodium hypochlorite solution. Complete dissolution results in a significant increase in the yield and specific activity of sodium 188W-tungstate. As an alternative approach, irradiated 186W-enriched metal targets dissolve in sodium hydroxide solution by cautious addition of < 30% hydrogen peroxide. Sodium 188W-tungstate solutions prepared from processing of such metal targets show no evidence of residual black insoluble material. Specific activity values for completely dissolved HFIR-irradiated 186W targets have increased to 10 mCi/mg (43.5 days) and 12.9 mCi/mg (49.2 days). Large clinical scale (> 1 Ci) generators prepared from hypochlorite-processed 186W oxide or peroxide-processed 186W metal targets exhibit the expected 188Re high yield and low 188W breakthrough.