Using a gamma camera regional pulmonary perfusion per unit alveolar volume (Q/VA) and ventilation-perfusion ratios (VA/Q) were measured in fourteen normal male volunteers in upright, supine, lateral decubitus, prone and prone suspended postures with inhalation and intravenous infusion of radioactive 81Krm (half-life 13 sec) and inhalation of radioactive 85Krm (half-life 4.4 h). In the vertical axis, Q/VA increased from upper to lower lung regions in upright, lateral decubitus, prone and prone suspended postures but was uniform in supine and within the dependent lung in decubitus postures. Horizontally, Q/VA decreased from cranial to caudal in lateral decubitus, prone suspended, and near the diaphragm in supine. Vertically, VA/Q decreased from upper to lower in all postures except in supine and within the dependent decubitus lung where it increased. VA/Q tended to increase from cranial to caudal in horizontal postures. The effects of gravity on Q/VA and VA/Q vertical distributions are modified when FRC is low (supine, lower decubitus lung) because perfusion is more uniformly distributed. Horizontal gradients of Q/VA and VA/Q are more pronounced under conditions of high local lung volume but also occur in postures where FRC is low.