Early tissue cultures of normal human lens cells show a differentiation of flat cells into fibre cells, which, at the periphery of the cultures, contain lysosomes with a high acid phosphatase activity. The microcinematography shows an adhesion between neighbouring fibres. Tissue cultures of cataracts show many cytolytic cells. Lysosome-like particles of several sizes and densities can be measured by morphometry. The lysosomal system probably plays an important role in senescence and cataractogenesis of the lens.