Two chromatographic methods were developed for the determination of erythromycin A (EA) residues in animal tissues (muscle, liver, kidney and fat of cattle, pigs and poultry) and cow's milk. In addition to a more traditional method using electrochemical detection, we developed an original alternative method based on UV detection at 236 nm, by pretreating to create a chromophore in the molecule. An internal standard was used with both methods to check the variability of the analytical system. Analysis times and performance were compared. The recovery of EA from various matrices was greater than 95%. For both methods the quantification limit for EA was 0.25 microgram ml-1 for plasma, 0.025 microgram g-1 for milk and 0.125 microgram g-1 for the other biological matrices. The methods can be used to check for EA residues in these matrices; in fact, the statutory maximum residue limits (MRLs) of EA are 0.4 microgram g-1 in muscle, kidney, liver and fat of beef cattle, sheep, pigs and poultry, and 0.04 microgram g-1 in cow's and sheep's milk.