Obama has a 60-second spot scheduled to begin airing tomorrow on 36 radio stations in that state that have predominantly black listenership.
The Illinois senator has been careful not to be defined strictly as a black candidate and risk alienating white voters. He and New York Senator Hillary Clinton are in a close fight for the black voters who traditionally make up half of the Democratic primary turnout in South Carolina.
The radio ad allows Obama to target his appeal to black audiences.
The ad uses parts of Obama's speech to the N-double-A-C-P. In it he discusses issues such as serious illnesses that disproportionately affect black patients.