The coincidental print-out by two different Laerdal(R) systems (subsequently called 'system A' and 'system B') of the same medical control module (MCM) for a Laerdal(R) Heartstart 2000 semi-automatic external defibrillator (SAED) led to the discovery of three deficiencies in the information storage and printing processes. First, we noted that the impedance reported via system A was consistently higher. Second, we found the attachment of 'mysterious' ECG samples in the reports from system B, but not from system A. A third problem was the unpredictable (in)ability of system B to print out the information from the MCMs. Further investigations with help from the company suggested that the above-mentioned problems were caused by incompatibilities between the software in the different parts of equipment used (i.e. SAED devices, MCMs, printing systems and a computer program to store the information in a database). These observations demonstrate the need for strict medical supervision on all aspects of a SAED project, and for feed-back from clinicians to manufacturers. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.