Tubulin purified from L cells by Sepharose 4B and DEAE-cellulose chromatography has properties similar to brain tubulin. The specific activity of colchicine binding is 1.1 mol of colchicine bound per 100,000 g of protein. From 0.07 to 0.45% of the total protein of L cells is active tubulin. Proteins differing biochemically from tubulin but coelectrophoresing with it in sodium dodecyl sulfate gels were encountered. Colchicine-binding activity of virustransformed NRK fibroblasts measured by a filter assay using a whole cell homogenate was reduced when compared to the parent NRK cells. L cells growing on plastic or glass surfaces had five times as much colchicine-binding activity as the same cells growing in spinner culture. Apparently growth on a surface increases the tubulin content of L cells.