Upon rehydration of the moss Tortula ruralis following desiccation at a rapid or slow rate, there is increasing utilization of newly synthesized-poly(A)(+) RNA for protein synthesis. Initially, poly(A)(+) RNA conserved in the dry moss is associated with polysomes, but by 2 hours of rehydration there is an overwhelming recruitment of newly synthesized poly(A)(+) RNA, at the expense of conserved messages. In rehydrated moss, there is a marked synthesis in vivo of new proteins, which are separable by two-dimensional electrophoresis, and identifiable by fluorography. These new proteins, termed rehydration proteins, are synthesized after both rapid and slow desiccation, but their synthesis persists longer after rapid desiccation. The protein patterns obtained following in vitro translation of bulk RNA from hydrated, desiccated, and rehydrated moss were qualitatively identical. Thus the differences in protein patterns observed in vivo must result from preferential selection of specific mRNAs from the same pool, which is indicative of control of protein synthesis at the translational level. The implications of these observations in relation to the response of the moss to drying in its natural environment are discussed.