Density data for dilute aqueous solutions of two isomeric aminobenzoic acids and of o-diaminobenzene (1,2-diaminobenzene) are presented together with partial molar volumes calculated from the experimental data. The measurements were performed at temperatures from 298.15 K up to either 498.15 K (aminobenzoic acids) or 573.15 K (o-diaminobenzene) and at either atmospheric pressure, or at pressures close to the saturated vapour pressure of water, and also at pressure p = 30 MPa. The data were obtained using either a high-temperature and high-pressure flow vibrating-tube densimeter for measurements at elevated pressures or a commercial vibrating-tube cell DMA 602HT for measurements at atmospheric pressure.