Sixty-nine patients with diffuse lung uptake of Tc-99m- tin colloid were evaluated to determine the kinds of associated diseases, the incidence of associated liver scan abnormalities, and prognosis. The results were as follows: 1) Diseases (associated with dliffuse lung uptake included malignancies in 3l patients, infectious diseases in 19, chronic liver diseases in 14, and others in 5, It appeared that the marked degree of lung uptake was associated with severe diseases. 2) Thirty- one of the 69 patients(45%) had abnormal liver size, 43(62%) had space occupying lesions or nonhomogeneity in liver image, 37(54%) had splenomegaly and 45(65%) had increased splenic uptake. In creased bone marrow uptake was found in 48(70%) and renal uptake in 15(22%). As the degree of lung uptake increased, there was a statistically significant (p〈0.05) tendency for the incidences of the abnormal liver image and renal uptake to increase. 3) Sixty-two of the 69 patients were followed up for one to 439 days (mean 44 days) after liver scanning. Eleven(l8%) were dead, 10(16%) were aggravated, and 13(21%) were improved. Most of improved patients had infectious diseases. It appeared that diffuse lung uptake of Tc-99m-Tn colloid was found in the various diseases including malignancies, infections, and chronic liver diseases, and that it was strongly associated with other liver scan abnormalities, but was not necessarily associated with a poor prognosis, particularly when underlying diseases were infections.