The capillary gas chromatographic (GC) analysis of silicon(IV), aluminium(III), gallium(III) and rhodium(III) alkyl substituted porphyrins, mainly as their trimethylsiloxy-derivatives, is reported. Retention indices on apolar stationary phases are presented and are discussed in terms of retention index increments associated with molecular differences between various porphyrins. The dependence of retention volumes (indices) upon the oxidation state of (and hence axial ligation to) the central metal is illustrated. GC-mass spectrometric (MS) data indicate that the silicon derivatives in particular are favourably suited to GC-MS analysis and the strong diagnostic ions produced under electron impact ionisation should prove invaluable for the analysis of complex mixtures. GC traces for the M(III) and for some of the silicon(IV) porphyrins are the first examples to be reported in the literature.