INTRODUCTION 1 2 3 Death from wasp envenomation is a rare event and results from acute renal failure (ARF) involving various mechanisms. Although ARF after wasp stings is typically caused by ATN in the setting of haemolysis or rhabdomyolysis, in some patients, renal failure may result from a direct nephrotoxicity of wasp venom or acute interstitial nephritis from a hypersensitivity reaction. We here we report two cases of acute renal failure after wasp stings (Vespa affinis). CASE 1 Table 1 CASE 2 Fig. 1 Table 1 OBSERVATION DISCUSSION Wasp stings are well-known causes of toxic and hypersensitivity reactions. Direct toxicity is rare, but has been reported in cases when a very large amount of venom is injected. Immediate hypersensitivity reactions, such as bronchospasm in the first case and an urticarial rash in the second, are known to occur. In our report, both reactions responded to steroids and antihistaminics. The second patient had swollen joints indicating serum sickness-like reaction in a sensitized individual. 4 5 6 7 8 9 10 11 In the first case we presented, the patient had myalgia, indicating muscle injury as evidenced by elevated CPK, LDH and AST and myoglobinuria (728 ng/ml). He also had intravascular haemolysis and haemoglobinuria. Toxic pigments might have caused nephropathy resulting in ARF. The alternative mechanism of ARF postulated was direct nephrotoxicity by massive wasp venom. 12 CONCLUSION Wasp stings pose a great environmental hazard in Nepal and early recognition of anaphylactic shock, hepatic or renal dysfunction, rhabdomyolysis or haemolysis and rapid transport to hospital are essential steps of management to avoid fatalities. ARF due to toxic or pigment nephropathy and tubulointerstitial nephritis should be considered in any oliguric and azotemic patient following wasp attack.