Abstract Introduction/objective Xerostomia is one of the main symptoms of primary Sjögren's syndrome (pSS). The unstimulated salivary flow (UWS) test is one of the objective Sjögren's syndrome classification criteria used to assess xerostomia's severity. The study’s objective was to evaluate UWS rate measurements (with a threshold rate of 0.1 mL/min) in the screening of patients suspected with pSS, presenting with xerostomia in whom labial salivary gland biopsy (LSGB) should be performed. We will try to answer whether it is possible not to perform LSGB in targeted patients according to UWS results? We analyze the correlation between UWS value and focus score (FS) and anti-SSA antibodies. Methods The study group consisted of subjects above 18 years of age with a subjective feeling of oral dryness. Results A total of 105 subjects were qualified for the study. The final diagnosis of pSS was made in 44 patients according to the classification criteria from 2016. No age differences were identified between pSS patients and control group subjects (patients with dry mouth without autoimmune background). UWS rates were significantly lower in pSS patients than in the control group. No association was identified between UWS and focus score (FS) ≥ 1 in LSGB. No differences were observed between anti-SSA-positive and anti-SSA-negative patients in terms of age, UWS rates, FS. Conclusion LSGB should be performed in all suspected pSS cases regardless of the UWS rate value, particularly in subjects without specific anti-SSA antibodies. In patients with suspected pSS, only less than one-half of the UWS measurements are below the value of 0.1 mL/min adopted as the threshold in the classification criteria for pSS.