The nuclear magnetic resonance relaxation times T1 and T2 of liver and spleen from freshly euthanized rats were measured over 48 hours for samples treated with normal saline, fixed with 70% ethanol, neutral buffered formalin, or 10% formalin, or left untreated. The initial values of T1 and T2 for both tissues agreed with previous determinations. For untreated tissues of both liver and spleen, T1 was stable for 6 hours and T2 was stable for 48 hours. For fixed tissues, T1 was stable for 0.5 hours, but T2 changed in 0.5 hours.