Fine needle aspiration specimens from 29 patients with bone and soft tissue neoplasms were analyzed by flow cytometry for DNA index and cell cycle analysis to determine whether such studies were helpful in cytologic diagnosis. Of 15 cases initially cytologically diagnosed as benign, 14 had a DNA index of 1.0, indicating a diploid population. The remaining case diagnosed as cytologically benign had a DNA index of 1.3. Further tissue from this tumor revealed an osteogenic sarcoma. Of the 14 cases initially diagnosed as malignant, 12 were hyperdiploid. Cell cycle analysis showed that malignant tumors had a higher proportion of cells in S phase (15.2% +/- 8.7%) than benign tumors (6.9% +/- 1.6%). Furthermore, high-grade malignancies had a significantly greater number of cells in S phase (18.5% +/- 1.5%) than low-grade tumors (9.9% +/- 6.3%).