In this study an enzyme-linked immunosorbent assay (ELISA) was developed to detect the stress protein Hsp70 in the green alga Raphidocelis subcapitata. Using this ELISA, the response to a variety of pollutants, including ZnCl2, SeO2 (heavy metals), lindane (organochlorine pesticide), pentachlorophenol (PCP, chlorinated hydrocarbon insecticide and fungicide), carbaryl (carbamate pesticide) and sodium dodecyl sulphate (SDS; surfactant) was tested. Our results show that Hsp 70 is produced in a dose-dependent way in response to most chemicals investigated (except PCP) and at concentrations below the range of classical cytotoxicity testing (i.e. growth inhibition, lethality). Still, the potential to induce Hsp70 varied among the pollutants tested, the heavy metals ZnCl2 and SeO2 being the strongest inducers of Hsp70. Combined with the existing literature, these results indicate that Hsp70 in R. subcapitata is a sensitive biomarker for a wide range of environmental pollutants. (C) 1998 Elsevier Science Ltd. All rights reserved.