Block error rate (BLER) measurements are made on a mobile telephone handset without imposing an undesirable processing burden on the handset. An information block flow is maintained by sending repeated message blocks from a test set which are defined at a selected layer in the protocol stack below the topmost layer. Ack/nack messages sent by the handset in response to the message blocks are monitored to determine whether the message blocks have been correctly transported, and thus derive the BLER. The message blocks sent by the test set can either be empty GMM_INFORMATION messages, or LLC frames with invalid frame check sequences.