This study investigated the use of lysosomal responses of hemocytes of the common garden snail, Helix aspersa, as biomarker of stress due to exposure to the fungicide copper oxychloride. The neutral red retention (NRR) time assay was employed for this purpose. Two groups of snails were exposed to 80 microg g(-1) and 240 microg g(-1) copper oxychloride in their food, respectively, for a period of 6 weeks. They were compared with a control group to which no copper oxychloride was added. The two groups exposed to the fungicide exhibited significantly higher (p < 0.001) whole body copper concentrations (200.85 +/- 53.5 and 272.24 +/- 67.15 microg g(-1) dry mass, respectively), and significantly shorter (p < 0.001) NRR times (10.22 +/- 3.53 and 2.67 +/- 2.83 min, respectively), after 6 weeks, compared to the control group (67.85 +/- 31.08 microg g(-1) dry mass and 24.44 +/- 8.35 min). In both exposure groups NRR times became progressively shorter as body copper concentrations increased over time. Thus, both exposure concentration and exposure time of copper oxychloride were shown to be important factors influencing lysosomal responses (and therefore NRR times) of H. aspersa hemocytes. It was concluded that these responses in this species, as measured by the NRR time assay, could be considered a useful cellular biomarker of stress resulting from exposure to copper oxychloride.