The adsorption transitions of a single self-avoiding polymer chain at chemically heterogeneous surfaces have been investigated using Monte Carlo methods and analyzed using scaling arguments. Evidence is provided that the crossover exponent phi, characterizing the transition between the weakly and the strongly adsorbed states, depends linearly on the dilution 0.6 less than or equal to p less than or equal to 1 of adsorbing sites on the surface, phi(p) approximate to 0.35 + 0.2p. The transition temperatures of chains of length N scale according to T-c(N,p)/T-c((infinity),p) similar to N- phi(p). In particular, we have analyzed the adsorption energies and the parallel and perpendicular components of the end-to-end distance.