Candiduria may signify benign saprophytic colonization or true infection of the urinary tract. Histological studies of 64 suspect cases of renal candidiasis, 20 of them positive, suggest that a Candida colony count of 10,000 to 15,000 per ml. or more in a catheterized specimen is a useful cut-off point between infection and colonization. One to 3 Candida per high power field in an uncentrifuged urine specimen equated with a colony count of 10,000 to 15,000 Candida per ml. Colony counts were diagnostically invalid in the presence of an indwelling Foley catheter. Other diagnostic aids included positive serum precipitin tests (83%) and positive blood cultures (47%).