OBJECTIVE Many findings suggest that in altricial mammals neonatal REM sleep has developmental functions. However, investigations of these developmental functions has been hampered by technical limitations of the conventional polysomnographic (PSG) recording technique. One limitation is that continuous (24 hour/day), long-term (weeks) PSG recordings have not been achieved. A second limitation is that the metal screw electrodes and head plugs cemented to the skull cannot be removed to allow the neonate to mature into adulthood. As a result of these limitations, the relationship between neonatal sleep/wake variables and adult variables has not been studied. Also the effects of polysomnographically controlled neonatal REM sleep deprivation on adult variables have not been studied. The present work describes a new technique called the soft head plug (SH) method for continuous, long-term PSG recording. METHODS In the new technique, electrodes are thin, strong, Teflon wires that are led by a suturing needle through the soft skull to the epidural space, then with a U-turn exited from the skull and tied to the entry wire. Thus, in contrast to the conventional technique, the soft head plug technique does not use screws as electrodes and does not cement a hard, relatively large electrode plug to the skull, removal of which is fatal or very traumatic. The SH recording electrodes can be removed without damage to neonates. METHODS NA. METHODS NA. METHODS NA. RESULTS In the present study sleep/wake results with the soft head plug technique were reliable (replicated) and, compared with results of the conventional method, valid. CONCLUSIONS The results indicate that the soft head plug technique can be used to study relationships between neonatal sleep/wake variables and adult variables.