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Eighty-four male white leghorn chickens were killed by CO2 gas to determine the type, rate, and sequence of postmortem microscopic changes in the kidneys of dry and wet intact carcasses. They were held at 29 or 18 C with 50% relative humidity for different times postmortem. Microscopic postmortem changes in the different segments of the nephron underwent a different rate and sequence of cellular changes. Cellular changes occurred earlier at 29 C than at 18 C and earlier in chickens not wetted with detergent solution. The decrease in body temperature of wetted chickens over dry chickens was significant (P less than 0.05). The proximal convoluted tubule (PCT) underwent the earliest postmortem changes, followed by the distal convoluted tubule (DCT), collecting tubule (CT), medullary loop (ML), medullary collecting duct (MCD), and glomerulus. The PCT, DCT, and thin and thick segments of the ML underwent a sequential nuclear change of chromatin margination, progressive shrinkage, pyknosis, karyorrhexis, and karyolysis. Nuclei were pyknotic if cytoplasmic changes were severe. Primary karyorrhexis was the predominant feature of collecting tubules and ducts. As early as one hour after death, some PCT cells of all kidney sections were pyknotic, emphasizing that immediate tissue fixation was necessary for critical evaluation. By 9 and 18 hr postmortem, PCT of dry and wet chickens, respectively, held at 29 C had pyknotic and karyorrhectic nuclei with slight karyolysis and moderate to marked cytoplasmolysis that extended until 36 hr. At this time, DCT were hardly distinguishable because of loss of basophilia. Karyorrhectic nuclei were already evident in collecting tubules and ducts. At 48 hr postmortem, all tubular cells were non-nucleated with homogeneous, acidophilic cytoplasm. Basement membranes no longer stained with periodic acid-Schiff (PAS). Erythrocytes were pyknotic with unstained cytoplasm. Pyknotic glomeruli were first observed at 9 hr postmortem in dry chickens and 12 hr in wet chickens. Histologic appearance of dry chickens at 9 hr and wet chickens at 18 hr when held at 29 C was similar to that of dry chickens at 12 hr and wet chickens at 24 hr when held at 18 C, with minor differences in some tubular changes. At 18 C, pyknotic glomeruli appeared by 6 hr in dry chickens and 24 hr in wet chickens. Widespread bacterial invasion was noted at 72 hr in dry chickens and at 96 hr in wet chickens.(ABSTRACT TRUNCATED AT 400 WORDS)