Measurements made with a towed thermistor chain in the thermohaline staircase east of Barbados show that the thick salt finger interfaces have horizontally coherent vertical fine structure. In an extreme form this interfacial substructure resembles a ''mini-staircase'' with several thin, high-gradient subinterfaces separating 2-m-thick sublayers which appear to be stirred by convective plumes. Signals from a simultaneously towed microstructure probe are consistent with previous models of salt fingers. Finger wavelength roughly follows the expected dT/dz-0.25 dependence; Cox number values associated with the fingers are most commonly between 10 and 20, independent of dT/dz; and finger amplitude increases roughly as dT/dz0.75, where dT/dz is the local vertical temperature gradient. ¿ American Geophysical Union 1989