We hypothesized that chlorogenic acids, the main phenolics in coffee, many fruits and Ilex paraguariensis extracts, protect paraoxonase 1 activity in HDL from inactivation by chlorination at concentrations of HOCl (50 microM) and chlorogenic acid (2-10 microM) compatible with those found in humans. When human HDL was incubated in the presence of HOCl/OCl-, a concentration dependent loss of activity was apparent. Of interest, 5 caffeoylquinic acid at 5 micromol/L affords more than 60% protection of the activity reaching 100% at 25 micromol/L. This compound and the plant sources that are rich in them may be protectors of paraoxonase 1 activity.