OBJECTIVE Turbidimetric urine protein methods like Benzethonium Chloride (BTC) and Benzalkonium Chloride (BC) are previously reported to give falsely low protein results in very high protein concentrations (>2000 mg/L). METHODS BTC and BC assays were adapted to an Olympus AU 640 analyzer in order to investigate the effect of the secondary wavelength on the linearity of the assays. Pyrogallol red (PYR) was also adapted to the same analyzer and used as the comparative method. RESULTS The linearity of BC was increased from 1500 mg/L to 3000 mg/L and the linearity of BTC was increased from 1500 mg/L to 2500 mg/L with the omission of the secondary wavelength. CONCLUSIONS We propose single-wavelength measurements for BC and BTC methods; however, urine samples with protein concentration >2500 mg/L for BTC and >3000 mg/L for BC should be diluted to appropriate concentrations.