In primary cultures verapamil affects a previously described aggregation phenomenon of bovine lens epithelial cells as well as the flattening of the aggregated cells Both enhancement of aggregation and delay of flattening are suggested to be caused by an interference of the drug with cell-capsule contacts. The harmful concentrations of verapamil are 100–1,000 times higher than those which may be reached in clinical uses. The usefulness of capsule-epithelium preparations in primary culture for toxicological tests is discussed