Phenol-formaldehyde mixtures are widely used in a variety of applications, such as flame-retardant or adhesives. This kind of resin can also be used as surface protecting polymers for glassy carbon electrodes when they are applied to phenol oxidative processes. The purpose of this work was to obtain the best conditions for phenol (and two derivatives) determination with a phenol-formaldehyde modified glassy carbon electrode in flow injection analysis (FIA) with amperometric detection and to compare these results with those obtained with two different modifiers, 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid, under the same conditions. Linear relationships were obtained in the 0.1 to 1.0 mu M phenol (or derivative) concentration range, the optima experimental conditions being 1.11 ml min(-1), 0.700 V (vs. Ag/AgCl/NaCl 3 M), with an electrodeposited charge of the modifier of 1.10 C cm(-2) and using an aqueous buffer (0.10 M total phosphate+0.05 M KCl, pH=7.0) as carrier solution.