A pH titrimetric study of the complexation of the guests benzoic acid, 4-methylbenzoic acid and (R)- and (S)-2-phenylpropanoic acids and their conjugate bases by the host 6A-[2-(2-aminoethylamino)ethylamino]-, 6A-[3-(3-aminopropylamino)propylamino]-, 6A-(1,4,7-triazacyclononan-1-yl)-, and 6A-(1,5,9-triazacyclododecan-1-yl)-6 A-deoxy-β-cyclodextrins (βCDdien, βCDdipn, βCDtacn and βCDtacdo, respectively) is reported. Over the pH range 3.0-11.0, 49 host-guest complexes were detected. Their stability constants (K) range from 220±50 dm3 mol-1 for the βCDdienH2 2+·benzoate- complex to 48000±11000 dm3 mol-1 for the βCDdipnH3 3+·(S)-2-phenylpropanoic acid complex at 298.2 K and I = 0.10 mol dm-3 (NaClO4). The latter K value is among the highest reported for a complex of a simple carboxylic acid with a substituted β-cyclodextrin. The charge, hydrophobicity and stereochemistry of both host and guest appear to be significant factors in the variation of host-guest complex stability. 1H ROESY n.m.r. studies of some of the complexes formed are also reported.