A biosensor based on carbon paste modified with crude extract of cara root (Dioscorea bulbifera) is proposed for the determination of epinephrine and dopamine in pharmaceutical formulations. After selection of the extraction medium, a crude extract of cara root was used as enzymatic source ofpolyphenol oxidase(PPO;tyrosinase; catechol oxidase; E.C:1.14.18.1). This enzyme catalyses the oxidation of epinephrine and dopamine to corresponding epinephrinequinone and dopaminequinone. A voltammetric study was performed by scanning the potential between +0.4 and −0.4 V. This biosensor provides a linear response for epinephrine in the concentration range from 2.0 × 10−4to 1.2 × 10−3mol L−1at Epc= −0.14 V (electrochemical reduction of epinechrome to epinephrine) and for dopamine in the concentration range from 2.0 × 10−3to 8.0 × 10−3mol L−1at Epc= +0.15 V (electrochemical reduction of dopaminequinone to dopamine). The detection limit (three times the signal blank/slope) was 8.2 × 10−5mol L−1and 7.5 × 10−4mol L−1for epinephrine and dopamine, respectively. The accuracy was checked by comparing with a Pharmacopoeia procedure and a paired-t test showing that all results obtained for these catecholamines in pharmaceutical products are in agreement at the 95% confidence level. The new biosensors have a longer lifetime than those prepared from purified enzyme.