A sulfuric acid–EDTA method for extracting ATP from soil and marine sediments was devised. The efficacy of this method is compared to the boiling Tris extraction procedure. Efficiency of ATP recovery from solid substrates typically ranged between 81–94% for the sulfuric acid–EDTA procedure in comparison to a recovery of 3–6% using boiling Tris buffer. The presence of various ions in the acid extract, however, inhibited light emission in the luciferin–luciferase measurement of ATP. Addition of EDTA to the extract reduced but did not eliminate the ionic interference. An internal ATP standard was thus used to determine the magnitude of the residual interference.