['(1) To determine whether children and elderly exhibit the atypical kinetics of very low frequency (VLF) power found in young adults, (2) to test the hypothesis that variations in "delta" bandwidth designations can explain discrepancies in whether normalized delta power density declines across non-rapid eye movement periods (NREMPs) linearly or shows the curvature expected of exponential change, and (3) to test our hypothesis that the decline in normailized delta power density in children across NREMPs would have a slope similar to that which we had previously found in young adults and elderly.', 'In 3 age groups (mean ages 11, 22, and 71 years) NREM electroencephalograms were analyzed with fast Fourier transform for frequencies between 0.3 and 4 Hz in bands. Across-NREMP trends of normalized power density for various "delta" bands were analyzed by analyses of variance for linearity, curvature, and age interactions.', 'We replicated the atypical kinetics of VLF power (-0.3-0.9 Hz) in young adults reported by others and showed that this pattern exists in children and normal elderly. As frequencies increased above 0.7 Hz, power showed first a linear and then a concave-upward curvilinear decline across NREMPs in children and young adults; the decline across NREMPS in the elderly became linear but never developed curvilinearity. For all designations of delta, the across-NREMP decline in children was significantly steeper than in young adults.'] Do kinetics of NREM delta EEG power density across NREM periods depend on age and on delta-band designation?