The vitamin A derivative, retinoic acid (RA) has various biological effects in mammalian cells and tissues. It is well known that RA induces differentiation of leukemia cells and inhibits cell growth. There are two pathways for RA action; one via RA nuclear receptors (RARs), and one via acylation of proteins by RA (retinoylation). However, an understanding of which actions of RA occur via RARs and which occur via retinoylation is lacking. Thus, we undertook the examination of HL60 proteins using anti-RA monoclonal antibodies (ARMAs). These ARMAs showed specific binding to proteins in a saturable manner depending on protein and antibody concentration. Proteins eluted by Mono Q anion exchange chromatography and separated using two-dimensional polyacrylamide gel electrophoresis were detected by ARMAs. One of these ARMA-bound proteins in HL60 cells was identified as alpha-actinin. These results indicate that retinoylated proteins in HL60 cells can be recognized by ARMAs and that alpha-actinin modified by RA may play a significant role in RA-induced differentiation, including the promotion of cytomorphology changes.