In this paper, the trans influence of boryl ligands, together with that of other ligands commonly believed to have a strong trans influence, has been investigated theoretically via density functional theory (DFT) calculations on a series of square-planar platinum(II) complexes of the form trans-[PtL(Cl) (PMe3)(2)]. The following order of trans influence has been obtained: -BMe2 > -SiMe3 > -BH2 > -SnMe3 - -BNHCH2CH(2)NH > -Bpin > -BOCH2CH2O > -BOCH=CHO similar to -Bcat similar to -BCl2 similar to -BBr2 similar to -SiH3 > -CH2CH3 > -CH=CH2 > -H similar to -Me > -C6H5 > -SiCl3 > -SnCl3 > -C-equivalent to CH. Natural bond order analyses have been used to understand how the substituents at the boron center affect the trans-influence properties of the boryl ligands. The major factor is the a-donor strength of the boryl ligand. However, surprisingly, very strong pi acceptors also enhance the trans influence.