THE D-threo isomer of chloramphenicol is an antibiotic and a specific inhibitor of protein synthesis in bacteria1. It also inhibits protein synthesis (net synthesis or turnover) in higher plants2-6, including cell-free systems7,8. Suppression of the induced increase in oxygen uptake in potato disks by D-chloramphenicol9 has been considered as indirect evidence of an inhibition of protein (possibly cytochrome oxidase) synthesis. Enzyme development during germination was also inhibited by D-chloramphenicol10,11. Recently, this chemical has also been used in several systems to relate ion uptake to protein synthesis in higher plants2,3,6,12-16. Others oppose this interpretation17-20. Meanwhile, the extrapolation of information on chloramphenicol from bacteria to higher plant systems has been criticized4,18. Ellis18, for example, observed that D-chloramphenicol did not affect incorporation of amino-acids into protein (trichloroacetic acid (TCA)-insoluble fraction) and yet it reduced ion uptake in higher plants. In contrast, the L-threo-isomer of chloramphenicol, which is neither an antibiotic nor an inhibitor of protein synthesis in bacterial systems, does inhibit ion uptake18 and root growth21 in higher plants. Thus, further elucidation was necessary as to the action of chloramphenicol as an inhibitor of ion uptake via an effect on protein synthesis.