The simultaneous determination of albendazole (ABZ) and praziquantel (PZQ) was performed by different mathematical approaches: second derivative spectrophotometry (SDS), classical least squares, regression of partial least squares and principal components regression based on spectral data of drugs dissolved in methanol-hydrochloric acid solution. The detection limits for multivariate calibrations were determined by creating a surrogate variable signal. SDS presented the best analytical features. The recoveries of ABZ and PZQ from the synthetic samples were near to 100 +/- 5%. The methods were applied in veterinary pharmaceutical formulation whose mass ratio ABZ:PZQ is 10:1; the results obtained were according to nominal content.