Monte Carlo simulation (MC) and quantum mechanics (QM) calculations based on the MP2 method were used to study the first hyperpolarizability (beta(HRS)) of retinal and retinoic acid isomers in protic and aprotic solvents. It is found that the first hyperpolarizability of the isomers can be considerably affected by the nature of solvent. For the all-trans retinal and retinoic acid isomers in methanol, the S-MC/MP2/6-31+ G(d) approach predicts for bHRS static values of 56 x 10(30) and 36 x 10(30) esu, respectively, which are in good agreement with the available experimental results. (C) 2014 Elsevier B.V. All rights reserved.