Objectives: The aim of this cross-sectional study was to investigate the relationship between minor salivary gland (MSG) flow rates and oral dryness degrees in patients with xerostomia induced by primary Sjogren's syndrome (pSS), IgG4-related sialadenitis (IgG4-RS), radiation therapy-induced dry mouth (RTDM), or Steven-Johnson syndrome (SJS). Design: 160 patients with pSS, IgG4-RS, RTDM, or SJS and their age- and sex-matched healthy control subjects were enrolled. The whole saliva flow rates and MSG flow rates were measured in four locations, including the upper labial, lower labial, buccal, and palatal mucosae. The degree of oral dryness was assessed in patient groups using the summated xerostomia inventory (SXI). Results: The flow rates of whole saliva and most MSGs in patient groups were significantly lower than the flow rates in healthy control groups (P < 0.05). The mean relative percentage of decrease in saliva flow rates was smaller in MSGs than in whole saliva in patient groups (P < 0.05), indicating that these disorders have less impact on MSGs. Among the four MSG locations (the upper labial, lower labial, buccal, and palatal), buccal glands showed the highest flow rates in patient groups (P < 0.05). SXI scores were significantly higher in pSS and RTDM patients than in IgG4-RS and SJS patients (P < 0.05). The degree of xerostomia varied among different patient groups (P < 0.05) and there was no clear correlation between MSG flow rates and SXI scores (P > 0.05). Conclusions: MSG function is significantly reduced in pSS, RTDM, IgG4-RS, and SJS patients, but this reduction is more pronounced in the major salivary glands. (C) 2016 Published by Elsevier Ltd.