BACKGROUND: There is increasing evidence of the benefit of regular physical exercise in a number of long-term conditions including chronic kidney disease (CKD). In CKD, this evidence has mostly come from studies in end stage patients receiving regular dialysis. There is little evidence in pre-dialysis patients with CKD Stages 4 and 5. METHODS: A prospective study compared the benefits of 6 months regular walking in 40 pre-dialysis patients with CKD Stages 4 and 5. Twenty of them were the exercising group and were compared to 20 patients who were continuing with usual physical activity. In addition, the 40 patients were randomized to receive additional oral sodium bicarbonate (target venous bicarbonate 29 mmol/L) or continue with previous sodium bicarbonate treatment (target 24 mmol/L). RESULTS: Improvements noted after 1 month were sustained to 6 months in the 18 of 20 who completed the exercise study. These included improvements in exercise tolerance (reduced exertion to achieve the same activity), weight loss, improved cardiovascular reactivity, avoiding an increase in blood pressure medication and improvements in quality of health and life and uraemic symptom scores assessed by questionnaire. Sodium bicarbonate supplementation did not produce any significant alterations. CONCLUSIONS: This study provides further support for the broad benefits of aerobic physical exercise in CKD. More studies are needed to understand the mechanisms of these benefits, to study whether resistance exercise will add to the benefit and to evaluate strategies to promote sustained lifestyle changes, that could ensure continued increase in habitual daily physical activity levels.