Adult male hooded (Long-Evans) rats (Rattus norvergicus) were used to compare the efficiency of three types of tests (plain open field – OF, open field with a refuge – OD, and complex environment with a refuge – EX), for the evaluation of exploratory behaviour. The results confirmed that OF is a highly aversive situation with the animals showing elevated emotional response (defecation and urination) when compared to situations containing a refuge (OD and EX). Presence of a plain arena (OF and OD) does not elicit high exploratory performance, as shown by the delayed and reduced exit from the refuge in OD when compared to EX. Thus locomotor activity in OF (covered distance, number of rearings) probably reflects more of an escape reaction than a genuine exploratory behaviour. Conversely the presence of a complex environment seems to elicit a high exploratory performance expressed as a quick exit from the refuge, an increased time in the environment (more than 75% of the observation time) and intense locomotor patterns (large covered distances, great number of rearings) but with little emotional display (reduced defecation and urination). The results thus show the importance of considering ethological factors in the choice or development of laboratory tests.