Acquisition of pictorial information and its retention over a one week retention interval were examined in 3 split-brain patients using the titration procedure developed by Huppert and Piercy (1978, 1979). Split-brain patients were found to have a normal ability to retain information once learnt. However, two of the patients required longer than normal presentation rates to reach the desired level of learning, suggesting the presence of an acquisition defect. In contrast, the youngest patient (L.B.) showed normal acquisition as well as normal retention. These findings are compared with those obtained for two classes of amnesic patients, i.e. Korsakoff patients and H.M., who show functionally different forms of organic amnesia. The results suggest that inter-hemispheric co-operation is relatively unimportant for normal retention although co-operation may be necessary for normal learning. The possibility of recovery of memory following commissurotomy is raised.