Each project in this Program deals with one aspect of respiration during the development of the individual organism. Project A is investigating the effects of exercise upon gas transport and fetal growth and development, using pregnant human subjects and Pygmy goats. Project B is concerned with the effects of diminished uterine blood flow upon the growth and development of the fetus, using guinea pigs as experimental models. Project D centers upon the effects of variations in the oxygen concentration of incubator gas upon the growth and development of the avian embryo before and after hatching. The investigators in Project E are measuring fetal cardiac output, its distribution and its control, using a chronically catheterized fetal sheep preparation. Project F is concerned with understanding the control of fetal water balance in chronically catheterized sheep and chronically prepared guinea pigs, and Project J focuses upon the effects of respiratory depressants and stimulants, comparing their effects in pregnant humans and animals with those in non-pregnant individuals of the same species. In addition to these individual projects, the Program has a core support system which includes conferences and guest professorships, a blood-gas laboratory, an animal facility, a computer facility, a radiation facility, and a central office for keeping the accounts, typing the manuscripts and progress reports, and scheduling patients for studies and the use of other core facilities.