The electron deficiency (hole concentration) in the La2-xSrxCuO4- system is determined by a chemical method. Our results show a direct correlation between Tc and hole concentration. The hole concentration equals the Sr concentration to about x=0.15. For x>0.15, the hole concentration decreases and oxygen vacancies are formed. These results strongly support an all-electronic mechanism for superconductivity in this system. © 1987 The American Physical Society.