Summary Water stress is found to reduce the incorporation of 32 p into different fractions of nucleic acids in the desert plant Anastatica hierochuntica . This reduction occurs within 24 hours after irrigation is stopped. Reirrigation after a hard water stress recovers nucleic acid synthesis within 12 hours. Comparisons of these data with analyses of the influence of water stress on the hormone balance of Anastatica hierochuntica (earlier results) suggest that there is a causal relationship between water stress, phytohormone content and nucleic acid synthesis.