Physicochemical studies of differences between normal and tumor-producing cells include: 1) The evaluation of morphological differences between normal and transformed hepatocytes by electron microscopy. 2) The study of changes in the kinetic behavior of lactate dehydrogenase isoenzymes (LDH) from these cells as a source of the increased excretion of acid observed upon transformation. 3) The comparison of kinetic and electrophoretic behavior of LDH isoenzymes in normal and transformed hepatocytes. 4) The analysis of this enzyme from mammalian tissue sources for comparison of electrophoretic and kinetic behavior with cells grown in culture and for clinical application of the methodology. 5) The methods were developed using LDH-1, -2 and -3 isolated from grey matter from exsanguinated rabbit brain. These results indicate that the kinetic behavior of isoenzymes from different tissues is unique and cannot be predicted on the basis of parallel migration in an electrical field. 6) The study of the effect of cyclocytidine upon DNA repair in normal and xeroderma pigmentosum human fibroblasts (in collaboration with R. Setlow).