The results of a tracer experiment conducted in a single fracture are interpreted using a semianalytical model which accounts for advective dispersion, matrix diffusion, mixing in the test zones, and for tortuosity. The experiment was conducted using a conservative tracer which was injected into a steady divergent flow field. Arrival of tracer was monitored in an array of 13 boreholes intersecting the fracture over a square area of approximately 30 m on a side. The arrival of tracer was detected in 11 of the 13 boreholes. Simulation of the transport process suggests that matrix diffusion may play a significant role in the migration of solutes. Contrary to previously published results, the relative influence of advective dispersion was found to be increasingly diminished with increasing scale. Fracture apertures determined from the results of the tracer experiment were found to be in general agreement with apertures calculated from independent hydraulic tests. The individual advective processes that contribute to advective dispersion remain unresolved on the basis of this experiment. ¿ American Geophysical Union 1993