The effect of pulverized plastic and glass-ceramic materials (methylmetacrylate, MMA), which are used as implantation materials in surgical medicine, on cell growth, DNA synthesis rate (adjudged by incorporation of 3H-thymidine into DNA), glucose consumption and lactate production (glycolytic rate) was studied in asynchronous monolayer cultures of rather fast proliferating Ehrlich ascites tumor cells and rather slowly proliferating diploid human fibroblasts. Exposure of Ehrlich ascites cells to high concentrations (2 mg/ml; 10 ml medium per culture) of ceramic or plastic material resulted in a gradual inhibition of cell growth and DNA synthesis rate. Protein synthesis, as measured by the incorporation of 3H-leucine, was somewhat less affected than DNA synthesis. Also, the glycolytic rate of Ehrlich ascites cells was slightly but significantly decreased in the presence of 2 mg/ml ceramics or MMA. Exposure of Ehrlich ascites cells to 0.2 or 0.02 mg/ml over a period of 46 h revealed none or only slight inhibitory effects on growth, DNA synthesis or glycolytic rate. On the other side, growth, DNA synthesis and glycolytic rates of human fibroblasts were nearly not affected by the presence of the same concentrations (up to 2 mg/ml, incubation period: 92 h) of pulverized ceramic or plastic material (MMA). It is suggested that this differential cellular sensitivity might be related to differences in the binding (to the cell surface) or uptake of these substances and possibly to differential intracellular lysosomal activation.