Eighteen patients aged between 55 and 65 and affected by respiratory insufficient were included in the study. Serum levels of PTH, total calcium, Ca++ and phosphorus were measured. Special attention was focused on PTH concentrations with in some case provedo to be above normal. Two hypotheses of pathogenesis are put forward. The first suggests that reduced Ca++ levels are responsible for anomalous PTH serum concentrations, whereas the second suggests that this role may be played by hypoxia. The latter would indirectly or directly affect parathyroids, either increasing PTH hyperincretion or slowing down the metabolism of the hormone by kidneys and liver which are in turn negatively affected by low blood oxygen tension.