Although monkeys are capable of solving problem-box tasks, they were said to perform without ‘understanding the value of unlocking’ and to use ‘kinesthetic control’ only [Kohts, 1928]. However, the cognitive processes are much more complex – at least in Cebus monkeys: the problem-solving process was conducted according to the position of the catch in relation to the edge of the door, i.e. our monkey learnt to use visual control. The main characteristics of the monkey’s behavior were similar to those exhibited by children. Problem-box tasks proved to be a suitable method for the comparative analysis of cognitive processes in primates.