Measurements of very low-frequency (VLF) atmospherics were made simultaneously at California and the Island of Hawaii. A third station in the source area in Oklahoma aided in locating each individual lightning event. From the differences in measured field strengths at the two remote stations the transmission loss as a function of frequency was determined for 37 waveform pairs. The average measured transmission loss was then compared to that predicted numerically using several exponential ionospheric conductivity models described by an inverse scale height &bgr; and reference height h' [in the notation of Wait and Spies (1965)>. Based on a weighted least-squares analysis of the calculated and measured data an appropriate ionospheric conductivity model (&bgr;=0.35 km-1, h'=72 km) was chosen which best predicts the measured daytime east-west transmission loss for a selected frequency band 7 kHz-18 kHz.