Actin plays an important physiological role in muscle contraction, cell motility, cytoskeletal structure, cell division, intracellular transport and cell differentiation. Total RNA was isolated from the thirdinstar larval body of Mamestra brassicae L. and Agrotis cnigrum. The two actin cDNA sequences were cloned by RTPCR and rapid amplification of cDNA ends (RACE). The M. brassicae actincDNA, 1 441 base pairs in length, contained an open reading frame of 1 131 base pairs coding for a olypeptide of 376 amino acid residues with a predicted molecular weight of 41.8 kDa. The A. cnigrum actin cDNA, 1 411 base pairs in length, contained an open reading frame of   1 131 base pairs coding for a polypeptide of 376 amino acid residues with a predicted molecular weight of 41.9 kDa. The two deduced amino acid sequences of actin were predicted using the software Prosite , which showed that they have three actin signature fragments. Blast search in GenBank and sequence comparisons with actin amino acid sequences from other species suggested that the A. cnigrum actin cDNA sequence encoded a cytoplasmic actin, and the M. brassicae actin cDNA sequence encoded a muscle actin. The two actin cDNA sequences have been deposited in GenBank with the accession nos. EU035314 and EU035315, respectively. Transcript analysis of A. c-nigrum actin during arious developmental stages and in different tissues was determined by RTPCR. A specific product was obtained from the integument, midgut and fat bodies from the third to sixthinstar larval stage and the pupal stage.