The changes in strength and internal structure of concrete exposed to pressure while plastic have been studied through two series of experiments. The results of the first series of tests indicate that cavities appearing under the aggregates due to local segregation are reduced in number and size with increasing level of pressure applied to fresh concrete. Pressure also causes a better compaction under the aggregates and thus improves the bond between the aggregates and the paste as well as the strength of the mass. It can explain the excess of strength increase in pressed concrete beyond what can be accounted for considering only the reduction of voids. Based on the results of the second series of tests, an empirical expression predicting the variation of strength along the depth of deep members due to variation of pressure head has been suggested. Comparisons have been made between these predicted values and reported in situ measurements of strength.