Inhaled nitric oxide (iNO) is used to treat a number of disease processes. Although in vitro data suggest that nitric oxide (NO) alters surfactant protein gene expression, the effects in vivo have not been studied. The objective of this study was to evaluate the effects of iNO on surfactant protein (SP)-A, -B, and -C gene expression in the intact lamb. Thirteen 4-wk-old lambs were mechanically ventilated with 21% oxygen and received iNO at 40 ppm (n = 7) or vehicle gas (n = 6) for 24 h. Peripheral lung biopsies were obtained at 0, 12, and 24 h and analyzed for surfactant mRNA, protein, and total DNA content. Inhaled NO increased SP-A and SP-B mRNA content by 80% from 0 to 12 h and by 78 and 71%, respectively, from 0 to 24 h. There was an increase in SP-A and SP-B protein content by 45% from 0 to 12 h, and a decrease by 70 and 65%, respectively, from 0 to 24 h. DNA content was unchanged. The mechanisms and physiological effects of these findings warrant further investigation.