Abstract. Cranberry is a popular fruit due to reported health benefits, but fruit rot and root rot diseases can decrease fruit production and quality. To determine the influence of infections, p-coumaric acid and quercetin derivatives which contribute to fruit quality were used as markers. Several cultivars including Stevens (ST), Mullica Queen (MQ), and Demoranville (DM) were sampled in MA during 2016 growing season. Analytical methods were developed for these markers in leaf and fruit with Waters UPLC-MS/MS system. Exposure to the two types of pathogens produced different responses. ST showed significant higher content in p-coumaric acid and quercetin derivatives when exposed to Phytophthora and significant lower content in these compounds when exposed to fruit rot fungi. For cultivars MQ and DM, healthy and infected plants exhibited less differences in phenolic composition, suggesting these cultivars may be less susceptible to fruit rot fungi than ST. Principal component analysis of the mass spectra confirmed several p-coumaric acid and quercetin derivatives as contributors to the variations in composition between the healthy and infected samples. This poster is not available for downloading.