In this work a new electrospray system has been developed which employs heat as a means of desolvation and requires no counterflow of heated gas. This article describes the operation and performance of this device, with particular emphasis on the differences between it and those described earlier. Results are presented that illustrate the dependence of signal intensity on ion source and spray chamber temperatures and on the composition and flow rate of mobile phase into the electrospray. Results on proteins electrosprayed from aqueous solutions are presented including a bacterial protease which has a tight tertiary structure. The ability to obtain fragmentation data by collisionally induced dissociation in the interface is also discussed.