Nitric oxide (NO) is produced at high levels by inducible nitric oxide synthase (iNOS) during inflammation and other pathological conditions, contributing to development of cardiovascular diseases. The present study determined if aging affects the ability of interleukin-1β (IL-1β), a pro-inflammatory cytokine, to induce increased NO production (assessed by Griess reaction) and iNOS mRNA levels (assessed by RT-PCR/agarose gel electrophoresis) in vascular smooth muscle cells (VSMCs) from young (3-month-old) and elderly (20-22-month-old) rats. The VSMCs cells were used only in early passages (passages 0 and 1) to avoid phenotypic modulation. To uncover subtle differences in basal iNOS mRNA levels in VSMCs of young and elderly rats, RT-PCR products were also analyzed by a new ultrasensitive technique using capillary electrophoresis with laser-induced fluorescence detector (CE-LIF). IL-1β (5 ng/ml) significantly (P<0.05) increased NO production 3.7-fold in elderly female VSMCs and 6.7-fold in elderly male VSMCs, but had no detectable effect in young female and male VSMCs. Basal iNOS mRNA levels (assessed by RT-PCR/CE-LIF) were dramatically higher in VSMCs of elderly male rats compared to young ones. In general, VSMCs of elderly rats showed much greater sensitively to iNOS-inducing actions of IL-1β. These data give new insight into effects of aging on iNOS expression in VSMCs, showing dramatic increases in both basal and stimulated iNOS mRNA levels, which may contribute to the development of vascular diseases in the elderly. Copyright © 2004 Published by Elsevier Inc.