Four rice (Oryza sativa) genomic actin genes have been characterized. The rice actin genes show a conservation of intron number and position that is characteristic of plant actins. Sequence comparisons revealed that the plant actins generally have a high degree of inter- and intraspecific sequence heterogeneity. However, one rice actin gene has a much higher degree of nucleotide sequence identity to a previously isolated actin sequence from Arabidopsis thaliana than to any other plant actin gene. This leads us to suggest that the two sequences may represent functionally homologous genes which arose from an ancient actin gene lineage that was separated by the divergence of the dicot and monocot plants. Genomic DNA blot analysis showed that the rice actin gene family contains at least eight unique members. RNA hybridization analysis revealed that individual rice actin genes can display different patterns of transcript accumulation. The observed differences in sequence and transcript accumulation patterns suggest that the individual rice actin genes may differ in their transcriptional regulation and/or cellular function.