Using ³¹P-NMR to study the high energy phosphates of mouse L₇₈₁₁ ascites cells with thymic ceils from 615 line mouse as control. The results showed there was clear differences between them.Even in the late stage of growth, L₇₈₁₁ ascites cells was not completely in an inactive state. For example, the ratio of phosphocreatine (PCr) and α-, β-, γ- adenosine triphosphate (α-, β-, γ-ATP) to phosphate (Pi) was greatly decreased but not completely inactive. The ratio of sugar phosphate (Sp) to phosphocholine (Pcho) plus phosphoethanolamine (PEtn) increased, while glycero(3) phosphocholine (GroPCho) plus glycero(3) phosphoelhano-lamine (Gro PEtn) decreased. Preliminary studies showed that ³¹P-NMR spectra are sensitive monitor to the progressive changes of the high energy phosphate metabolism of the L₇₈₁₁ ascites growth.