The cationic amphiphile meso-tetrakis (1-octyloxycarbonylmethyl-4-pyridinio) porphyrin has been prepared by quaternization of tetra(4-pyridyl) porphyrin . Its self-aggregation into columnar face-to-face stacks is indicated by n.m.r. and electronic absorption spectra in chloroform and chloroform/methanol mixtures. In 10 mole % CD3OD/CDCl3 solution, concentration-dependent dimerization occurs, with an association constant Kd 5.81×103 dm3 mol-1. In pure methanol, chemical shifts are concentration dependent, but do not fit a simple dimerization model. In water/methanol mixtures, aggregation occurs so that the hydrocarbon chains approach the porphyrin core, but the macrocycles do not stack in a face-to-face manner.