Specific globin mRNA accumulation was quantitated in several lines of K562 cells in the absence and the presence of hemin. Using specific cloned DNA probes, the amounts of zeta, alpha, epsilon and gamma mRNAs were shown to be increased 2–3-fold in the presence of 20 microM hemin. No delta- or beta-globin mRNAs were detectable in any of the lines. In one line, Bos, there was a marked decrease in epsilon-globin mRNA, which increased with hemin, although still to much lower levels than in the other lines. The decreased epsilon-globin mRNA accumulation in Bos is shown to be due to decreased epsilon-globin gene transcription.