Although many anecdotal opinions are available that water gives a better visual quality, no studies have analysed the differences in the visual quality of the operative field with the use of either saline or sterile water. As part of a prospective audit we wished to assess the effect of differing irrigant fluids on intraoperative visibility during Greenlight photoselective vapourization of prostate (PVP). Twenty-nine consecutive patients with prostates less than 100 cm(3) who underwent PVP were studied. The irrigation fluid used was randomly connected on a bag-by-bag basis, with the surgeon blinded to the bag's contents. Towards the end of each bag the surgeon gave a score to the quality of vision. All surgeons were familiarized with the vision scoring system in advance. The scores were analysed in two ways. The mean scores for water and saline were compared. In addition, a mean score for each fluid in each patient where both fluids were used (n=24) was separately calculated and the means for each fluid compared. One hundred and twenty-four bags of fluid in 29 operative cases were analysed. The mean overall vision scores were 3.94% for saline and 4.01% for water (P=0.62). The paired data were analysed using the Student's t-test and there was no statistically significant difference (P=0.34). We showed no significant difference in visual quality between water and saline during PVP. Although fluid absorption is almost unknown with PVP, there seems to be no justification for using water irrigation if saline is available, particularly with a theoretical risk of absorption.