Conductivity, temperature, and depth data from the 15 quasi-monthly cruises of the Hawaii-Tahiti Shuttle Experiment are used to document fine-structure variability in the upper 400 m of the central equatorial Pacific. The analysis reveals the existence of anomalously strong temperature and density variations on 0(1--10 m) vertical scales concentrated in the high mean shear zones of the equatorial current system and in the thermostad These are regions where microscale measuremens also indicate intense turbulent activity. The implication of this spatial correspondence between large-, fine-, and microscale signals is that there may be a cascade of energy from the largest to the smallest scales of variability that is mediated by fine-structure processes. The highly structured fine-scale signal suggests that the cascade would be most pronounced and persistent on certain density surfaces that lie within the regions of highest mean shear. Other processes, such as wind stirring, air-sea buoyancy exchange, and intrusions, also contribute to the generation of fine-structure variability and mixing at equatorial latitudes. There is evidence, for example, that intrusions across the sharp equatorial salinity front in the upper 150--200 m account for 10%--20% of the fine-structure temperature variance and more than 50% of the fine-structure salinity variance. The dominant vertical scale of these intrusions appears to be ≲10 m and the cross-frontal scale <100 km. A simple model calculation of cross-frontal mixing indicates that they are important in transferring heat and salt laterally across the front. Intrusions in the vicinity of the Equatorial Undercurrent core may support salt fingering; hence they may contribute to vertical transports of salt and heat in a region where turbulent mixing is weak.