Using only three measures of the waveform, the zero-crossing rate, the logarithm of the root-mean-square (rms) energy, and the derivative of the log rms energy with respect to time [termed rate of rise (ROR)], voiceless plosives (including affricates) can be distinguished from voiceless fricatives in word-initial, medial, and final positions. Peaks in the ROR contour are considered for significance to the plosive/fricative distinction by examining the log rms energy and zero-crossing rate. Then, the magnitude of the first significant peak in the ROR contour is used as the primary classifier. The algorithm was tested on 1364 tokens (720 word-initial tokens produced by four female and four male speakers; 360 word-medial tokens produced by two males and two females; 320 word-final tokens produced by two males and two females). Data from two male and two female speakers (360 word-initial tokens) were used as a training set, and the remaining data were used as a test set. The overall rate of correct classification was 96.8%. Implications of this result are discussed.