The purpose of this study was to evaluate the toxicity of Spirulina maxima, a blue-green alga used as food supplement and food coloring, after 13 weeks of treatment. Groups of ten mice of each sex were given S. maxima in the diet at concentrations of 0 (control), 10, 20 or 30% (w/w) for 13 weeks. The alga ingestion had no effect on behavior, food and water intake, growth or survival. Terminal values in hematology and clinical chemistry did not reveal differences between treated and control groups. However, male and female mice showed significant changes in serum cholesterol levels at 20 and 30% algal concentrations, but a toxic effect of S. maxima was excluded. Post-mortem examination revealed no differences in gross or microscopic findings. Our results show that S. maxima up to high feeding levels did not produce adverse effects in mice after subchronic treatment. Copyright (C) 1998 Elsevier Science Ireland Ltd.