The uptake of white blood cells (WBC) into normal bone marrow may lead to difficulty in detecting bone infection. Twenty-one patients in whom the WBC scan was equivocal or positive underwent a technetium 99m colloid scan to show the distribution of bone marrow. Six patients had a positive WBC scan, and in five of them a discordant colloid scan confirmed infection. However, in one the colloid scan was concordant, indicating that the WBC activity was not due to infection but the result of normal bone marrow uptake. Fifteen patients had an equivocal WBC scan. In 14, infection was excluded by a concordant scan, and 1 patient with a discordant scan was lost to follow-up. We conclude that the combination of a WBC scan and a colloid scan is an effective method to distinguish infection from normal bone marrow activity and, in particular, reduces the number of incorrect diagnoses of infection.