Density functional calculations are employed in the study of the C-C bond formation step of an aldol reaction in presence of a series of metals. Focus was placed on first row d-block metals that have been used in catalysis of direct aldol reactions. The obtained energy profiles are analysed in order to differentiate between factors governing catalysis. Results demonstrate a major influence of d-orbital occupation, and suggest some of the so far less commonly used metals as promising candidates for development of new catalytic systems. (C) 2011 Elsevier B.V. All rights reserved.