To measure, compute, and learn to modify forces between cell membranes. We have succeeded in measuring the repulsion forces between membranes of the phospholipid lecithin. This has been possible by exerting an osmotic stress on a stack of membranes while doing x-ray diffraction to measure their spacing. Repulsion forces are mechanically large between these membranes and exceed two atmospheres even at 20 Angstrom separation. With the success of this method we are now introducing selected lipids bearing charge or sugars into the model membranes to measure systemic changes in membrane repulsion forces. We have found that small sugar solutes in the medium between model membrance apparently modify the van der Waals attraction forces which create the lamellar array. This effect of solvent has been predicted by the general theory of forces but not been seen before. Dr. D. Gingell has done two experiments that are a direct outgrowth of his work here in the DCRT. First, he has found red cell aggregation following precisely that predicted by modulating electric charge on the membrane surface. (His data were processed here at the DCRT during his visit last summer). Second, he has succeeded in designing a substrate to which cells may adhere which is at the same time an electrode to which attractive or repulsive potentials may be applied. He has demonstrated stable attraction of cell-to-substrate with an apparent gap between them. Modulation of the applied potential and observation of resultant cellular sticking or non-sticking will allow us to make quantitative estimates of cellular attraction forces.