In a controlled multi-center single-blind study, the relative efficacy and tolerance of i.m. injectable preparations of etofenamat(e) and diclofenac sodium were investigated in 96 patients with acute lumbago. Treatment resulted in obvious improvement in function and reduction in pain, no statistical difference being found between the two drugs. In 43% of the patients treated with etofenamat(e) and 27% of those receiving diclofenac, the final medical report indicated very good therapeutic results. Under etofenamat(e) i.m. therapy, no side effects occurred, and in no case did treatment have to be discontinued. Under diclofenac, two patients experienced adverse reactions, one allergic exanthema, and the other itching and a sensation of heat. A further patient experienced no improvement after the first injection and discontinued treatment.