The sterol fraction obtained from the unsaponifiable matter of oils of fishes commonly used in alimentary preserves has been studied. It is cholesterol (90-96%), 24-methylene-cholesterol (24MC) (1-4%) and several minor components. GLC relative retention times (RRT) with stationary phases SE30 and OV17 (TMS derivatives) of fish sterols have been compared with those of phytosterols in order to show eventual interferences when sterols of oils covering tinned fish have to be analyzed. The main interference is produced by 24MC, the RRT of which is near to that of campesterol with both SE30 and OV17. It can lower the apparent Beta-sitosterol content in the sterol fraction of a covering olive oil, from an original level, for instance, of 94% to minimum values of 89%, 80%, 90% (cholesterol excluded) respectively for tinned mackerels, sardines, tunny. Owing to its low R(, f), 24MC can be eliminated through a previous argentation-TLC, working on sterol acetylderivatives. In this way the 93% forensic limit for apparent Beta-sitosterol in the olive oil sterol fraction composition has to be considered as valid also for olive oils covering tinned fish.