Elucidation of sleep-endocrine relationships requires frequent blood sampling during sleep recording. Unfortunately, such sampling can itself affect sleep and indirectly, hormonal patterns. We examined the effect of catheterization and frequent nighttime blood sampling on the sleep of a large sample of healthy older men and women. A total of 113 healthy older [69.1 +/- 0.6 years, mean +/- standard error of the mean (SEM) adults (68 women and 45 men) were studied. Following an adaptation night sleep was recorded during an undisturbed night and a night of periodic blood sampling via i.v. catheter. Lights out and lights on were significantly delayed and advanced, respectively, on the catheterization night, resulting in a significantly shorter time in bed (TIB). Total sleep time and sleep efficiency were significantly reduced, and sleep latency, total wake time and the number of awakenings from sleep of > or = 1 minute were significantly increased. Rapid eye movement (REM) sleep percentage of TIB was significantly reduced. Stages 3/4 sleep [slow wave sleep (SWS)] percentage of TIB was significantly reduced, as was total delta energy during SWS. With the exception of total sleep time and sleep latency, all sleep-wake and delta variables were significantly correlated between nights. This was particularly the case for SWS and the delta energy variables. When examined separately by gender, both men and women showed significant catheter-based sleep disturbance. However, SWS and delta energy measures in men were unaffected by catheterization. The data clearly demonstrate that both the sleep maintenance and sleep architecture of healthy older men and women are significantly impacted by nighttime blood sampling procedures. Of the various measures examined here, SWS measures appear to be the least disrupted, particularly in men. These findings need to be taken into account in any study examining sleep-endocrine relationships utilizing older subjects.