The amperometric determination of phenol and catechol derivatives in general, and dopamine in particular, is studied, using enzymatically modified carbon paste electrodes. Both the electrochemical behaviour of the substrates and the enzymatic selectivity of polyphenol oxidase (PPO) according to the source are taken into account. In this way, the quantification of dopamine in the presence of metabolically related compounds is carried out with reasonable accuracy. Fresh tissues of pear, peach, mushroom and potato are used as the enzymatic For fresh mushroom PPO, apparent Michaelis-Menten constants (K-M’) for each substrate are determined electrochemically. Purified mushroom PPO is used for comparative purposes. The effect of the substituent group of catechol derivatives on the enzymatic affinity was also analysed.