Two nicotinic acid-related compounds were found to induce erythroid differentiation in K562 cells. We investigated the changes in nicotinamide adenine dinucleotide (NAD) content induced by nicotinic acid-related compounds during differentiation. The NAD content was reduced by a treatment with nicotinic acid and isonicotinic acid. These results provide important clues toward elucidating the erythroid differentiation mechanism.