Expression of the arylsulfatase (HpArs) gene in the sea urchin, Hemicentrotus pulcherrimus, is regulated in spatially, as well as temporally, during development. To address the cis-regulatory elements involved in this regulation, we performed reporter assays using variously deleted or mutated promoter and regulatory elements of the HpArs gene, accompanied by gel mobility shift assay and foot printing. Results show that two regions, PU1 (-72 b.p. to -56 b.p.), which is similar to SpZ12-1 and/or Oct-1 motif, and the PD1 site (+133 b.p. to +142 b.p.), which is homologous to the binding sites of Rel family transcription factors and/or AGIE-BP1, are related to the regulation of expression of the HpArs gene. Furthermore, an HpArs enhancer element called C15, which is located 3 kb.p. downstream from the transcription start site, activates the HpArs promoter. We also report that the enhancer activity of the C15 fragment was mediated by elements, PU1 and PD1.