In order that the results of experimental investigations of the flow of rocks may be applied with any degree of assurance to problems of rock deformation in nature, it is essential that the effects of all five of the varying environmental factors be investigated: (1) confining pressure, (2) shear stress, (3) temperature, (4) time, and (5) the presence of solutions. Pressure alone changes the behavior of rocks and simulates some types of natural deformation but is shown to be inadequate to explain all natural flow because of the tremendous strength increase involved, its inability to produce plastic behavior in quartz, and the development of too intense mechanical twinning in calcite aggregates. Temperature produced unimportant results in preliminary experiments at high pressure. Time seems to be inadequate as shown by creep tests on Solenhofen limestone at low and high pressure. Some new experiments show the effect of solutions. The properties of quartz change markedly in the presence of solutions at elevated temperatures. Marble flow is strikingly altered by the presence of solutions at elevated temperature. New creep tests on alabaster in the presence of solutions seem to demonstrate recrystallization flow and indicate the existence of two general laws governing this type of flow. These reconnaissance experiments indicate the important role that solution and recrystallization may play in rock deformation.