The prenylflavonoids 6-prenylnaringenin (6-PN) and 8-prenylnaringenin (8-PN) are secondary plant substances, almost exclusively found in hops (Humulus lupulus). Both compounds have known potential biological properties, but poor bioavailability due to their low oral absorption and retention. Our study followed a single dose (500 mg 6- or 8-PN), placebo controlled, randomized, double-blind, three armed crossover study design with ≥2-week washout periods. Plasma, PBMC and urine samples were collected at intervals up to 24 h after intake. Investigators investigated the safety, pharmacokinetics and impact of oral prenylflavonoids on the function of cells of the immune system.