Transient electromagnetic sounding methods (TEM)have several advantages over DC resistivity soundings. The principal advantage is that sounding depths several times the receiver-transmitter spacing can be achieved, resulting in less cumbersome field work and more flexible sounding site selection. The TEM method was tested using a commercially available instrument (Geonics EM-37)in the Gulf Springs region of west-central Florida to locate the saltwater interface in the Floridan Aquifer. The Floridan is a thick (200 m), unconfined, karstic, carbonate aquifer within the study area. High annual rainfall and internal drainage create a deep and dynamic interface. Eighty transient soundings were completed in 18 field days. Seventy-one soundings used a square 80 m × 80 m transmitter loop, and the other nine used a 160 m × 160 m coil. The interface was easily detected from a minimum depth of 60 m to its maximum depth of about 140 meters. Also, a high-resistivity, low-porosity zone was detected at depths ranging from 180-250 meters. The TEM data compare well with available chloride concentration data. The TEM interface corresponds to chloride values in excess of 200-400 mg/1. The sounding curves obtained suggest that with presently available instruments the TEM method is not well-suited for shallow soundings (less than 40-50 meters). Copyright © 1986, Wiley Blackwell. All rights reserved