K562 cells can be reversibly induced by hemin to accumulate embryonic and fetal hemoglobins. The increase in individual globin mRNAs accompanying induction was measured by isolation and in vitro translation of poly A+ RNA from both control and induced cells. epsilon-Globin mRNA showed the greatest increase (threefold) with hemin induction, followed by zeta greater than gamma greater than alpha. These results were corroborated by measuring steady-state mRNA concentrations by a recently developed S1 nuclease mapping procedure. Changes in epsilon-, gamma-, and alpha-globin levels parallel the changes measured by in vitro translation. S1 nuclease mapping studies revealed that epsilon-, gamma-, and alpha-globin transcripts were correctly initiated and processed. In addition, correctly initiated and processed delta-globin transcripts were detected at low levels, increasing 1.5-fold following hemin induction. However, no beta-globin transcripts could be detected by this sensitive and specific assay. The beta-globin gene may be under developmental control in K562 cells, and this cell line may therefore provide a unique assay system for molecules involved in globin gene regulation.