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We have studied the effect of triphenyl-lead chloride on the lipid phase of erythrocyte membranes, on lipid monomolecular layers and Na /K -ATPase of the microsomal fraction of rat brain. It was found that the haemolytic effect induced by this compound occurs when its concentration exceeds 30 mM. The minimal lead concentration inducing measurable effects in monomolecular lecithin layers is about 1 mM. Inhibition of Na /K -ATPase activity begins at a concentration exceeding 0.5 mM. Maximum inhibition is observed at around 40 mM-a concentration at which haemolysis also occurs. It can thus be thought that at very low lead concentrations the main (or exclusive) role in modifying membrane function is played by direct interaction between lead and the sulphydryl groups of ATPase, whereas at higher concentrations two effects seem to overlap: direct interaction between lead and enzymic proteins via their sulphydryl groups and as indirect influence on the proteins via changes in the organization of the lipid phase of the membrane.

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