Pair configurations of symmetric diblock copolymers in a selective solvent (i.e. a good solvent for one block and a Theta-solvent far the other block) and of their constituent homopolymers were investigated. Cubic lattice chains of total length N = 160 were generated by use of Monte Carlo methods. Pair data were determined by exact enumeration of all possible pair configurations. When the separation between two copolymer chains reached zero (r --> 0) the pair distribution function g(r) is about 0.18, which is slightly larger than the value found for athermal systems (approximate to 0.14) but appreciably smaller than g(0) of Theta-systems (0.6-0.8). The extent to which mean squared dimensions and shape parameters depend on intermolecular distance for block copolymers was similar to that of athermal chains, as well. Transformation of the data into a concentration dependence revealed that with increase in concentration chain dimensions decreased in the case of good and selective solvents while they increased for Theta-solvents. Concomitantly, the molecular shape became more globulelike in the former case, while it remained fairly unchanged in the latter. On the whole, diblock copolymers in a selective solvent were found to behave approximately like homopolymers in a relatively good solvent.