Taxol (Paclitaxol) is a diterpenoid taxane derivative found in the bark and needles of the Western yew, Taxus brevifolia, indigenous to the old growth forests of the Pacific Northwest. As compared with other antineoplastic agents (vinca alkaloids and colchicine) that enhance microtubule disassembly, taxol promotes microtubule polymerization. In interphase cells, abnormal microtubular bundles or arrays are seen. In mitotic cells, abnormal spindle asters form. Such morphologic changes have been described frequently in cell culture systems and in in vitro systems using fresh tumor tissue. To our knowledge, these changes have not been described in a peritoneal effusion specimen from a patient with stage III ovarian cancer treated with taxol. In addition, the mitotic stabilization produced interpretative difficulties in evaluating the peritoneal fluid because a vast majority of the presumed malignant cells were in mitosis and, hence, not evaluable by ordinary cytologic criteria.