Application of the Z-scan technique for the detection of CFCDNA (cell-free circulating DNA) and urine DNA (uDNA) in patients with bladder cancer. BACKGROUND:  Patients with BC have a higher amount of cell-free circulating DNA (CFCDNA) in the blood and urine than healthy people. We aimed to verify if the Z-Scan method could analyze the concentrations of uDNA (urinary) and pDNA (plasma) in relation to the time of collection during treatment for patients with bladder cancer. METHODS:  Peripheral blood and urine samples were obtained from 30 patients with BC at the time of diagnosis, 45, 90 and 180 days after initiating treatment; 5 μL of k-DNA (k = u or p) was added in 250 μL a solution of 1:1000 Ethidium Bromide dye (EtBr) in water. Continum laser Nd:YVO4, wavelength λ = 532 nm was used. Samples of uDNA and pDNA in water were submitted to the laser with an incident power of 84.5 mW and an exposure time of 30 ms. RESULTS:  There was a different concentration of pDNA and uDNA during the treatment of patients using both optical techniques. However, the reaction rate of pDNA and uDNA was similar with spectrophotometry, whereas the z-scan technique presented different values. CONCLUSION:  Z-scan technique has potential for use in the differentiation of pDNA and uDNA concentrations, which are distinct in patients with BC and healthy people.