The genetic basis for relationships among red blood cell antigens, isoenzyme types and physiological function will be studied. The relationships in pigs among genes which are associated with susceptibility to the porcine stress syndrome (PSS) will be used as a model. Expression of PSS as identified by development of muscular rigidity under halothane anesthesia (HAL plus) is associated with blood type in the A-O and H systems of red blood cell antigens and with PHI (phosphohexose isomerase) isoenzyme types, but the associations are not entirely consistent from population to population. There is close linkage between genes for H and PHI types, and these genes are also linked to genes for 6PGD isoenzyme types. Recombination among genes for PHI, HAL, H and 6PGD types as well as genes for inhibition of expression of A and O, will be measured among offspring from appropriate matings.