Domoic acid production was screened in the Nitzschia-like strains of benthic diatom collected from Ishigaki Island (subtropical area), Tohoku District of Japan (temperate area) and Manila Bay, the Philippines (tropical area). Domoic acid was detected in 88 out of 183 strains collected from these areas. The cellular domoic acid content of these strains ranged from 0.1 to 15.3 pg/cell. All the strains positive for domoic acid production were identified as Nitzschia navis-varingica, a new domoic acid-producing benthic diatom species that was recently found in Vietnam. This species was collected only from brackish water. These results indicate that domoic acid-producing N. navis-varingica is distributed widely in brackish water from tropical to temperate areas.