Melatonin in red wine (both Rioja and Ribera de Duero) was determined using the ELISA kit, with results ranging from 50 pg/mL to 80 pg/mL (Guerrero et al., in press). One hour after human volunteers had consumed 100 mL of red wine, the increase of melatonin in plasma was statistically significant. After consumption of 100 mL of white wine, no significant changes could be observed.