In parallel with the cytosolic and mitochondrial ATP measurements, we also monitored mitochondrial membrane potential (Δψm) by employing the membrane-permeant cationic fluorescent probe, TMRM, to determine whether mutations in KRAS and TP53 genes may affect, in human colon cancer cells, also this bioenergetic parameter in response to nutrients availability. The gene discussed is KRAS; the disease is malignant colon neoplasm.