The results of surveillance cultures in 424 neutropenic patients with hematologic malignancies were analyzed to evaluate the relationship between colonization and infection by Candida species. Eighteen (32%) of 56 patients with multiple noncontiguous colonized sites developed proven (13 cases) or probable (five cases) systemic candidiasis, versus two patients with proven candidiasis (1.2%) of 170 with one colonized site (P less than 0.00000001), and one patient with proven candidiasis (0.5%) of 198 without any evidence of Candida colonization (P less than 0.00000001). Twenty-two patients with multiple colonized sites who developed a febrile episode resistant to antibiotics were treated with empiric amphotericin B. Nine of 11 given empiric amphotericin B within day 6 survived versus three of 11 receiving antifungal therapy after day 6 (P = 0.014). The above data seem to justify further prospective studies on Candida colonization as indication to early antifungal therapy in febrile neutropenic patients.