Although it is recognized that a thorough understanding of the biology of incubation is important in the conservation of marine turtles, the difficulties entailed in obtaining measurements of the clutch environment have led to a paucity of data in this area. This paper describes the measurement of gas exchange and temperature from an array of points in the egg chambers of five loggerhead turtles on the beach at Mon Repos, Queensland, Australia. Water table level was also measured in the hatchery in which these turtle eggs were incubating. The result demonstrated a decrease in oxygen and an increase in carbon dioxide partial pressure in these clutches over the latter half of incubation. Small partial pressure differences between measurement points at the periphery of the egg chamber and the egg shaft in relation to the center of the clutches were found for oxygen and carbon dioxide. Temperatures on average in the egg chamgers of the control site and the experimental clutches followed the general pattern of the surface temperature and during the summer of 1986-87 clutch temperatures rose from approximately 26-33 C. Over the latter half of incubation there was an increase in the temperature at the center of the two experimental egg chambers in comparison with the control site. Daily variations in temperature were most evident on the surface with the variations becoming less as one moved towards the lower periphery of the clutch. Further, the water table level fell by 40 cm and followed the general tidal level in the 3-4 d observation periods. A daily periodic rhythm was also evident in the water table level. These data supplement our knowledge regarding the environment of development and demonstrate similar features to those reported in earlier studies.