Background: This paper presents results of in vitro trials of a wearable artificial kidney (WAK). Materials and methods: To carry out the trials, a test bench was developed. It consisted of a patient imitator, a tubing set and measuring equipment. Results: Our WAK can eliminate urea, uric acid and creatinine from spent dialysate with mean mass rates of 0.85 ± 0.1 g/h, 0.10 ± 0.04 g/h and 0.05 ± 0.01 g/h, respectively. Concentrations of Na+, Cl– and Ca2+ ions were kept in the 10% range from initial values. We demonstrated that our WAK can operate for 38 hours without having to replace expendable materials. Conclusions: The WAK that we developed can eliminate metabolites from spent dialysis fluid with mass rates that are sufficient to maintain stable, physiologically normal metabolite concentrations in patients’ blood.