The effectiveness of CT and technetium-99m sulfur colloid (99mTc SC) bone-marrow scans in determining the extent and severity of skeletal involvement in 23 patients with type 1 Gaucher's disease was compared with the effectiveness of conventional radiographic techniques and technetium-99m methylene diphosphonate (99mTc MDP) bone scintigrams. Density measurements obtained by CT proved sensitive in differentiating normal marrow (-50 to -120 H). Scintigrams with the sulfur colloid nuclide demonstrated three distinct patterns of uptake: (1) peripheral expansion of normal marrow (profile B), (2) greater marrow expansion with patchy areas lacking uptake (profile C), and (3) greater loss of uptake with retention of the nuclide in other reticuloendothelial organs and circulation (profile D). CT scans provided greater sensitivity in resolving the extent of marrow involvement in affected areas, while the 99mTc SC scintigrams were more effective in overall assessment of the severity of bone-marrow involvement. Both conventional radiographic techniques and 99mTc MDP bone scans were useful primarily as screening procedures or for evaluating specific involved areas. 99mTc MDP scans were useful in evaluating regional defects (i.e., ischemic necrosis) in certain cases, but no consistent patterns were observed. CT and 99mTc SC scans are useful for determining the extent and severity of Gaucher's disease involvement of bone marrow.