This study investigates the influence of training experiences on dogs' performance in a problem solving task, namely opening a box to obtain food. One hundred and eighteen dogs allocated to two different groups according to their training experience (no/basic training vs high level training) were tested. In each group the dogs saw the researcher manipulating either the paw-pad or the lid, prior to being allowed free access to the apparatus. No effect of the locus of manipulation was observed. However, there was a strong effect of training on the dogs' performance regardless of manipulation condition. Compared to untrained dogs, highly trained dogs were more successful in opening the box and spent significantly more time interacting with the apparatus; whereas untrained dogs spent significantly more time looking back at their owners and the researcher. These results indicate that high levels of training improve dogs' problem solving ability, with dogs appearing to be more proactive in the their interaction with novel objects.