Background/Aims: An unsuccessful colonoscopy procedure is often related to inadequate bowel cleansing. It is difficult for patients to finish the whole 4 liters of polyethylene glycol-electrolyte lavage (PEG-EL) because of its salty taste and the large quantity. Pineapple juice has been shown to be an effective agent in the dissolution of undigested food in the stomach. This study assessed the effectiveness of both 2 and 4 liters of PEG-EL in precolonoscopic bowel cleansing and the quality of colonoscopic cleaning by adding 1 liter of pineapple juice to a reduced-volume PEG-based regime. Methods: The patients were chosen from those undergoing a colonoscopic procedure. A total of 126 patients were randomized into 3 groups receiving 3 different PEG-EL (Golytely®) regimes, i.e. 4 liters of PEG-EL (group 1, n = 44), 2 liters of PEG-EL (group 2, n = 39) or 2 liters of PEG-EL with 1 liter of pineapple juice (Dimes® 100%; group 3, n = 43). Results: Both the 4- and 2-liter PEG-EL regimes resulted in similar bowel cleansing scores in all parts of the colonic segments. However, adding 1 liter of pineapple juice to the reduced-volume PEG-EL regime improved the quality of the cleansing on the right side of the colon and in the transverse colon. Adequate bowel cleansing was achieved in 68.1% of the patients in group 1, 63.9% in group 2 and 80% in group 3 (the lowest score in one of the segments). On the other hand, the tolerability of the regimes was similar in all 3 groups (p = 0.509). Conclusions: Reduced PEG-EL (2 rather than 4 liters) may be sufficient for precolonoscopic bowel cleansing in the Turkish population. Administration of pineapple juice in the reduced-dose preparation regime may improve the quality of the bowel cleaning.