Since fine needle aspiration (FNA) cytology has been rarely successful in preoperatively separating neoplastic from nonneoplastic (inflammatory and congenital) liver cysts, the adjunctive use of measurements of cyst fluid carcinoembryonic antigen (CEA) levels for enhancing the accuracy of the cytologic diagnosis was examined. FNA was performed on 17 consecutive cystic lesions from 15 patients. Cytologic examination performed on Papanicolaou-stained smears or Cytospins of the sediment gave a sensitivity of 66% and a specificity of 100%. CEA measurements on the supernatant by enzyme immunoassay showed negative levels (less than 5 ng/mL) in fluids from benign (nonmucinous) cysts and abscesses and elevated levels (greater than 600 ng/mL) in fluids from biliary cystadenoma/cystadenocarcinoma and pseudocystic metastatic carcinoma. CEA assay gave a sensitivity of 100% and a specificity of 94%, thus enhancing the sensitivity of FNA for the detection of malignancy in cystic liver lesions.