Twenty-eight patients undergoing rhinologic surgery were enrolled in a clinical study to compare two post-operative cleansing preparations. Patients were asked to wash their nasal fossae for 1 month, either with Rhinomer®, a cleansing preparation of isotonic, sterile, undiluted sea water, presented in a slightly pressurised bottle with neither CFC nor preservative, or with Prorhinel®, a marketed solution containing an antiseptic agent. Patients were randomly allocated to treatment beginning 2 days after surgery. Nasal status was assessed by symptoms (blocking nose, rhinorrhoea, sneezing, itching and impaired smell) and rhinologic endoscopy (colour of the nasal mucosa, swelling of the mucosa, secretions, presence of crusts or pus). Patients attended control visits on days 9, 15 and 30 following surgery. They were asked to record symptom intensity and use of a rescue medication (Vibrocil®, dimetindene 0.25 mg and phenylephrine 2.5 mg/ml) on a diary card. Twenty-six of 28 patients were eligible for efficacy analysis, 14 in the Rhinomer group and 12 in the Prorhinel group. In both groups, intensity of complaints decreased markedly over the study period. No severe adverse drug reactions were reported in either treatment. Evoked complaint frequency was comparable between groups, but patient’s and physician’s opinion on tolerability was significantly different between treatments, in favour of Rhinomer. In addition, the test preparation was found to be easier to use than Prorhinel. The weekly average frequency of use of the rescue medication was not significantly different between treatments. When both patients and physicians were asked about treatment efficacy, they expressed an opinion significantly more favourable to Rhinomer than to the reference drug. In this study, Rhinomer has shown efficacious results that justify its use in washing of the nasal cavities following endonasal surgery.