When 0.2-g pink salmon Oncorhynchus gorbuscha were carried by helicopter in Alaska, total gas pressure in the transport water reached 71.3 mm Hg (109.4% of barometric pressure). Gross and microscopic lesions in swim bladders of fish progressed during transport to tympanitic dilatation, then to separation of laminae and rupture. Other associated signs and lesions were exophthalmos, cranial swelling, edematous gill lamellae, hemoperitoneum, emphysema of the yolk sac, and distension and rupture of the yolk sac membrane. Rapid reduction of barometric pressure during the flight and the subsequent increase in dissolved-gas supersaturation caused gas bubble disease and tissue alterations that affected health and survival of the fish.