The uptake of 14C-1-glucosamine by HeLa cells and its subsequent fate has been studied. Over 90 per cent of the label initially taken up by the cells is found in the uridine diphosphate-N-acetylhexosamine pool. This pool loses its label in 12 hr and the radioactivity is found in the aminosugar residues of cell components. Eventually, two thirds of the label is secreted into the media as high molecular-weight compounds that contain aminosugar while one third of the label remains with the cells and is gradually metabolized. Labeling of cells in culture with glucosamine 14C provides a sensitive means for studying cell components that contain aminosugars.