Objective To investigate the efficacy and safety of the technique of instillation of normal saline prior to suction of airways in intubated patients. Data sources Databases searched included: MEDLINE, CINAHL, EMBASE, Cochrane Controlled Trials Register and Full text clinicians' health journals @ Ovid from the earliest time to March 2009. Citation tracking of relevant primary and review articles. Review methods All randomised controlled trials, crossover trials, quasi- and full systematic reviews were screened. From 65 articles screened, 17 articles (two quasi-systematic reviews and 15 empirical studies) met the eligibility criteria and were included for data extraction. The outcomes in the reviewed studies included oxygenation, lung mechanics, sputum yield, dyspnoea, tube patency and ventilator-associated pneumonia. Effect sizes and 95% confidence intervals were calculated. Results Studies were mainly of low methodological quality due to factors such as lack of assessor blinding and within-group-only statistics. Overall, there was a positive effect favouring the use of saline to increase sputum yield (d = 0.50, 95% confidence interval 0.10 to 0.90). Due to heterogeneity of methodology, it was not possible to perform meta-analyses on haemodynamics, oxygenation, tube patency and ventilator-associated pneumonia. Overall, while a decrease was found in oxygen saturation measured by pulse oximetry (SpO2) following instillation of normal saline compared with no saline, this was of limited clinical significance. Conclusions The results of this review reflect the poor quality of available articles on instillation of normal saline prior to suction of artificial airways. There is little evidence of benefit but also minimal evidence of safety risks. Controlled trials of better quality and more clinically relevant outcomes need to be performed before this technique is either accepted or rejected.