We have purified a cell growth factor from a human lung cancer cell line, T3M‐30, which was established in a protein‐free chemically defined medium. The factor, designated carcinoma‐derived growth factor (CD‐GF), stimulated proliferation of a variety of cells, including human leukemia cells, HL‐60, and melanoma cells, SK‐28. Half‐maximum stimulation by the purified CD‐GF was achieved at a concentration of 40 ng/ml. In the purified CD‐GF, two major protein bands of 24 kDa and 22 kDa were identified on a SDS polyacrylamide gel. The partial amino acid sequences of the 24 kDa protein were determined from two peptide fragments obtained by V8 protease treatment. The partial sequences were identical to those of heavy chain of human ferritin. The activity of the purified CD‐GF was coprecipitated completely with a monoclonal antibody to heavy chain of ferritin. Ferritin has been considered to inhibit cell growth. However, human heart ferritin was capable of stimulating the growth of HL‐60 cells. These results suggest that CD‐GF is related to feritin and ferritin is a growth factor of HL‐60 leukemia cells. © 1994 Wiley‐Liss, Inc.