Mean aerological data for Saigon during July 1966 and 1967 and for Udorn in 1967 are presented and compared with similar data for tropical maritime regions. The comparison indicates that level for level the atmosphere over Southeast Asia has greater humidity and higher static energy. Comparison of dewpoint profiles taken during periods of suppressed and increased convection over Southeast Asia reveals that the atmosphere is more moist during increased convection and that the diurnal variation of humidity is largest during suppressed conditions. Comparisons of vertical profiles of virtual equivalent potential temperature taken during periods of suppressed and increased convection show that the daily convective instability is strong during suppressed days and weak during days of increased convection. The characteristic differences in structure as shown, suggest convection is controlled by the synoptic scale.