Apparatus for recovering lost buffer contents in a data processing system uses a memory divided into a plurality of buffers provided with buffer control blocks, through which source and destination users exchange information. A buffer management circuit is responsive to requests from users for allocating buffers to source users in order that source users may store the information to be sent to the destination users. This circuit builds buffer queues and dequeues buffers from the queues to send the information contained therein to the destination users and releases the buffers afterwards. A time mark register is settable to n different values in a predetermined order. The value of the time mark register is changed at the expiration of a time period P. Each time a buffer is allocated to one user, the current value of the time mark register is written into a time mark field of the buffer control block and a state field is set to a first value (leased). When the buffer is released, the state field is set to a second value (released). The contents of the buffer control blocks are read at regular time intervals t after period P, and the state field of every buffer control block is tested to determine whether it is set to the second value. If not so set, the time mark field is compared with the value the time mark register had at the time t-xP, where x is a number such as 1