Measurement of the fraction of exhaled nitric oxide (FENO) provides a noninvasive way to monitor asthma treatment in clinical practice. The aim of this study was to determine FENO reference values for measurements recorded with the portable NIOX MINO monitor in a group of healthy volunteers. We also assessed the association between values recorded by the portable monitor and the N-6008 chemiluminescence analyzer used in our pulmonary function laboratory. The FENO values obtained with the portable monitor were consistently higher than those recorded by the N-6008 analyzer; the cutoff value for the portable monitor was 34 ppb (mean + 2 SD). We detected a direct correlation (r=0.92) between the FENO measurements recorded by the 2 monitors (P=.001). The following equation expresses the relationship between measurements from the 2 devices: FENO(NIOX MINO) = 10 + [1.5 FENO(N-6008)]. We did not observe statistically significant correlations between FENO measurements and age, sex, body mass index, or spirometry.