We prospectively investigated the ability of detection of antibodies to Candida albicans germ tubes (CAGT) to diagnose invasive candidiasis in 95 consecutive admissions of 73 patients with hematologic disorders undergoing intensive chemotherapy. The episodes were divided into three groups according to clinical and microbiological diagnosis. Group 1 comprised eight admissions of eight patients with invasive candidiasis. Group 2 comprised 42 admissions of 34 patients without evidence of invasive candidiasis. Group 3 comprised the remaining 45 admissions of 37 patients with febrile episodes which were not diagnosed by microbiological culture. Antibodies to CAGT were detected in 87.5% of group 1 patients. Detection of antibodies to CAGT in patients with Candida fungemia was delayed somewhat relative to the time the blood culture was positive, but antibodies to CAGT were detected earlier than a diagnosis was made in patients with deep-tissue candidiasis. Sera from 2 admissions in group 2 and 12 admissions in group 3 revealed antibodies to CAGT. At a titer of > or = 1:20, detection of antibodies to CAGT had a sensitivity of 87.5%, specificity of 95.2%, positive predictive value of 77.8%, and negative predictive value of 97.6%. Antibodies to CAGT were usually detected before beginning of empiric antifungal therapy. Titers of antibodies to CAGT were maintained in most patients who died but declined and eventually disappeared in the patients who survived. Since antibodies to CAGT were detected in all patients with tissue-proven invasive candidiasis but negative by blood culture, detection of antibodies to CAGT complemented blood cultures for diagnosis and therapeutic monitoring of patients with hematologic malignancies and invasive candidiasis.