On-line micro- and semimicro-HPLC/FT-IR interfaces have been developed in our laboratory. These interfaces involve thermospray nebulization of the HPLC effluent and a modification of the Bio-Rad Tracer direct deposition GC/FT-IR interface. The detection limits for on-line narrow-bore HPLC/FT-IR measurements are at the low nanogram level. The performance of reversed-phase HPLC/FT-IR was tested at flow rates from 8 to 50 μl/min. The modified fused-silica and stainless-steel transfer lines developed for HPLC/FT-IR can also be used for direct deposition GC/FT-IR measurements. The feasibility of using the same instrument for on-line HPLC/FT-IR and GC/FT-IR direct deposition measurements has been demonstrated.