A study has been made of freeze-fractured preparations of erythrocyte ghosts modified by phospholipase C (Clostridium welchii). Such membranes show a decrease in surface area of up to about 47% and lipid droplets appear on their external surface but there is no loss of protein. Freeze-fracture of maximally hydrolysed membranes exposes only very small areas of A faces and these appear particle-free. Most of the membranes are simply cross-fractured. At lower levels of hydrolysis there is more extensive exposure of A fracture faces but the particle density is less than in control preparations. If such exposed faces were representative of the whole membrane then the particle density would have been expected to increase. It is suggested either that areas of membrane with increased particle density do not fracture or that the particles revealed by freeze-fracture involve phospholipid as well as protein and are not revealed in the absence of phospholipid.

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