The determination of selenium in solid waste and the effluents of solid waste treatment systems is of considerable interest because of the toxicity of selenium and its reported presence in almost all conceivable types of paper. A 2,3-diaminonaphthalene (DAN) analytical procedure is preceded by isolation of selenium with toluene 3,4-dithiol and includes the use of EDTA, sodium fluoride and sodium oxalate masking agents. The reactions in the procedure are thought to involve the formation of a piazselenol. The piazselenol emits at 5700 A when excited at 3170 A. The use of the DAN fluorometric procedure affords the sensitivity necessary for trace analysis while retaining a precision of measurement comparable to competitive methods. The isolation step and masking agents are used to prevent background fluorescence and foreign ion effect.