The diffusion coefficient of cucurbit[6]uril (CB[6]) and cucurbit[7]uril (CB[7]) was determined using pulsed gradient spin-echo nuclear magnetic resonance spectroscopy. Both CB[6] and CB[7] diffuse faster through H(2)O than D(2)O with increasing temperature, consistent with the Stokes-Einstein equation where diffusion is proportional to temperature divided by viscosity. The activation energy (EA) was also determined and is larger for CB[n] in 90 % H(2)O/10 % D(2)O v/v than in D(2)O. Both compounds aggregate with increasing concentration between (0.25 and 2) . 10(-3) mol . L(-1). The pH of the solution does not significantly affect the diffusion coefficient of CB[6] and CB[7], except at very low pH where protonation of the carbonyl groups induces aggregation, which slows their rate of diffusion.