The essentiality of silicon in biology might be explained in the terms of its chemistry with aluminium. In a previous study we demonstrated the elimination of acute aluminium toxicity in fish by silicon. We suggested that the reaction of silicic acid with aluminium to form hydroxyaluminosilicates reduced the biological availability, and hence toxicity, of aluminium. Though assumed in a burgeoning number of studies and contended in others this detoxification mechanism has remained unproven. Herein we have tested the toxicity of hydroxyaluminosilicates in fish and in doing so we have provided evidence which strongly supports a role for hydroxyaluminiosilicates in the elimination of acute aluminium toxicity in fish by silicon.Copyright 1997 Academic Press Limited Copyright 1997 Academic Press Limited