Eosinophiluria is considered a useful marker of drug-induced acute interstitial nephritis. However, recognition of eosinophiluria by Wright's staining is technically difficult, and the spectrum of disorders causing eosinophiluria is not completely defined. We have adapted Hansel's stain for the examination of urinary sediment. Whereas there was a variable uptake of Wright's stain by eosinophils in the urine, such eosinophils were readily recognized with Hansel's stain by the presence of bright red granules. The prevalence of eosinophiluria in acute interstitial nephritis was 10 of 11 patients, in acute tubular necrosis none of 30, in acute pyelonephritis none of 10, in acute cystitis 1 of 15, in postinfectious glomerulonephritis 1 of 6, in rapidly progressive glomerulonephritis 4 of 10, and in acute prostatitis 6 of 10. Eosinophiluria in acute interstitial nephritis was demonstrated by Hansel's stain in 10 of 11 patients but by Wright's stain in only 2 of 11 patients. We conclude that Hansel's stain substantially improves the recognition of eosinophiluria as compared with Wright's stain. Eosinophiluria is useful in distinguishing acute interstitial nephritis from acute tubular necrosis. The clinical spectrum of eosinophiluria also includes rapidly progressive glomerulonephritis, acute prostatitis, and occasionally, acute cystitis or postinfectious glomerulonephritis.