Interdiffusion coefficients D-ao in octan-1-ol of benzene, toluene, chlorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, bromobenzene, 1,2-dibromobenzene, and 1,4-dibromobenzene have been measured at 25 degrees C at average solute mole fractions from 0.001 to 0.000 05 using the Taylor dispersion technique. The D-ao values range from 0.5 x 10(-9) m(2)/s to 0.3 x 10(-9) m(2)/s with standard deviations below 4% in all but the highest dilutions and show only minor (and statistically insignificant) variations with solute concentration. In addition, corresponding interdiffusion coefficients of methanol, ethanol, propan-1-ol, butan-1-ol, 2-methylpropan-2-ol and phenol were determined at average mole fractions around 0.0004. For both groups of compounds, distinct but separate dependencies of D-ao on molecular size were observed. The results are discussed from the viewpoint of the Stokes-Einstein equation, and in comparison with literature data for the corresponding diffusion in water. The analysis reveals different dependencies of the interdiffusion coefficients on solvent viscosity for the two classes of compounds. Current chemical engineering correlations to predict D-ao at high dilution (D-ao(infinity)) yield only moderate agreement for the benzenes and perform particularly poorly for the alcohols, suggesting that additional experimental work is needed to better understand molecular diffusion in more viscous media.