The purpose of this study was to determine the objective short-term influence of nasal continuous positive airway pressure (nCPAP) therapy, nasal mask leak (NML) and heated humidifiers (HH) to nasal conditioning of spontaneously breathing subjects. This was a prospective, non-randomized, non-blinded day-time study. Eighteen healthy subjects were enrolled in the study. All subjects received nCPAP therapy for 60 min in three different conditions successively: (1) nCPAP without humidification, (2) nCPAP with a defined leakage of nasal mask (slashed circle 28.3 mm2) and (3) nCPAP with HH. Nasal humidity and temperature were measured in the anterior turbinate area using a miniaturized thermocouple and a relative humidity sensor. The measurements were accomplished at the beginning of therapy, after 60, 120 and 180 min. Absolute humidity (aH) in the anterior turbinate area decreased significantly (p = 0.0075) from 17.41 +/- 3.81 mg/l (baseline) to 15.27 +/- 2.21 mg/l (nCPAP alone). With attachment of a NML, aH decreased from 15.27 mg/l not significantly (p = 0.058) to 13.77 +/- 2.28 mg/l (nCPAP and NML) compared to nCPAP alone. After addition of heated humidification to nCPAP, aH increased again from 13.77 mg/l significantly (p = 0.042) to 15.29 +/- 3.51 mg/l (nCPAP and HH) compared to aH (nCPAP+NML). No difference was found between aH (nCPAP and HH) and aH (nCPAP alone). Airway temperature did not change significantly after application of nCPAP alone, nCPAP and NML, and nCPAP and HH. These data indicate that nCPAP therapy with NML tends to have more remarkable reduction of the nasal humidity than nCPAP therapy without NML. nCPAP with heated humidifier is able to compensate the dehydration effects induced by nCPAP therapy with NML by increasing the aH at the anterior turbinate area to the levels observed during breathing with nCPAP alone.