In the chicken genome, downstream from the delta 1 gene, encoding delta-crystallin, a highly homologous gene called delta 2 is found, but neither its expression nor its function has been clarified. Close similarity of the delta 2 gene to mammalian argininosuccinate lyase (ASL)-encoding genes in organization and deduced amino acid sequence of the encoded protein suggested that this gene may encode chicken ASL. To test this possibility, we cloned the delta 2 gene on a plasmid, introduced it into mouse cells, and assessed expression and ASL activity in comparison with delta 1. We found that delta 2 was expressed well in fibroblastic L cells, which resulted in synthesis of a protein with a size (50 kDa) and antigenicity very close to delta-crystallin, but it was repressed in lens cells in which expression of delta 1 was activated. Transfectant L cell lines expressing delta 2 exhibited significantly higher ASL activity than those without. We conclude that the delta 2 gene codes for chicken ASL, but has a tissue specificity distinct from delta 1 in its expression.