The N,N'-diacid of meso-tetrakis(4-sulfonylphenyl)porphin forms both J- and H-aggregates. Both the B-and Q-transitions exhibit a J-band. Under typical experimental conditions, the monomer and H-bands are also observed. We have measured the pressure dependence of the various spectral bands up to 40 kbar. All data show linear dependence of spectral red shift with pressure. The monomer Soret band has the highest pressure sensitivity. The pressure slope of the B-band is 3.6 times greater than that for the e-band for the J-aggregates. A simple excitonic theory predicted a ratio of nearly Il. It appears that there is a substantial solvent shift contribution to these pressure derivatives. (C) 1997 American Institute of Physics.