Plasma phylloquinone (vitamin K1) concentration from non-fasted blood samples was examined by season, smoking status, socio-demographic factors and phylloquinone intake in a nationally representative sample of 1154 British individuals aged 19–64 years from the 2000–1 National Diet and Nutrition Survey. Geometric mean plasma phylloquinone concentration was 0·94 (95 % CI 0·88, 1·00) nmol/l, with 95 % of values in the range 0·10–8·72 nmol/l. Plasma phylloquinone concentrations of 530 men were significantly higher than those of 624 women (1·13 (95 % CI 1·04, 1·22) v. 0·81 (95 % CI 0·74, 0·88) nmol/l; P < 0·001), independent of other factors. Women aged 19–34 years had significantly lower plasma phylloquinone concentration than their older counterparts. Women were also found to have lower plasma phylloquinone concentrations during summer compared with winter and spring (each P < 0·01). In contrast, plasma phylloquinone concentration in men did not vary significantly by season or any of the socio-demographic or lifestyle factors. Plasma phylloquinone concentrations were positively correlated with phylloquinone intake in men and women (r 0·26 and 0·32 respectively; each P < 0·001). Overall, forward stepwise multiple regression analysis revealed that 8 % of the variation in plasma phylloquinone concentration was explained by phylloquinone intake, with a further 10 % of its variation explained by plasma concentrations of γ-tocopherol (6 %) and retinyl palmitate (4 %). After adjustment for age and corresponding nutrient intakes, plasma phylloquinone concentration was significantly associated (each P < 0·01) with plasma concentrations of total and LDL-cholesterol, α- and γ-tocopherols, retinyl palmitate, β-carotene, lycopene and lutein plus zeaxanthin in men and women.