The aim of the study was to evaluate the effect of repeated measurements on isokinetic lifting strength in a smaple of patients with low back pain. The measures were performed in series of five consecutive lifts on two occasions 1-13 days apart, and the patients continued their normal living during this period. A group of healthy subjects was used as a control. The hypothesis was that a mere repetition of the lifting procedure would increase the performance, and that the increase would be bigger in the patient group that in the non-patient group. In addition, grip strength was measured on both occasions. It was supposed that grip strength would not change from trial 1 to trial 2. The results showed an increase in lifting strength from first to second trial in the patient group by an average of 28%, and in the control group by an average of 16%. Grip strength did not increase in either group. The last of five consecutive lifts was the best one in a majority of the cases in both trials. Neither five consecutive lifts nor measurements on two different occassions seem enough to define a reliable baseline for maximal lifting capacity. Other factors than an increase in muscle strength influence the performance, one being a repetition of the lifting procedure. This must be accounted for when defining a baseline for isokinetic lifting capacity.