The sensitivity of the indirect Coombs’ test was investigated using saline, albumin,or low ionic strength (LIS) in the incubation phase and an incubation time varying from 5 to 120 min. Titration of 41 antibodies showed that LIS always resulted in a higher or almost the same mean scores as the other solutions after the same incubation time. The maximum mean score was always higher with LIS than with saline and was reached after a shorter period of incubation, only 20-40 min even with the weakest antibodies. With LIS, a longer incubation time than 40 min resulted in a sudden decrease in mean score. The maximum mean score using saline or albumin was reached after 40-60 min incubation. The same mean score was obtained after only 15-20 min, when LIS was used. Albumin gave only slightly higher mean scores than saline.