The study reports the results of the detection and quantitation of morphine in tissues fixed in formalin and in the formalin solutions in which the same tissues were fixed. Toxicological analyses were performed on formalin-fixed liver and kidney samples from five cases of opiate poisoning and on the formalin solutions (10% buffered pH 7) in which the samples were preserved. Analyses carried out at the time of autopsy on body fluids and tissues allowed identification of opiate as the cause of death and its quantitation. Tissue samples were preserved in formalin solutions for 12 weeks before analysis. The mean levels of recovery of morphine in fixed tissues were 36.29% in liver, 29.41% in kidney, 74.93% in formalin from liver, and 42.17% in formalin from kidney. Results indicated that this particular toxic substance shows good stability even in biological specimens subjected to chemical fixation.