In an attenlpt to develop two highly equivalent forms of a test of phonemic discrimination, two lists, each composed of 50 CNC monosyllabic words and conforming to the phonemic balance favored by Lehiste and Peterson (1959), were recorded on magnetic tape in six different word orders. These lists, designated as N. U. Auditory Test No. 4, were administered monaurally on a test-retest basis to 16 Ss with normal hearing, 16 with conductive losses, and 16 with sensori-neural impairments. An interval of 1 to 2 wk. separated the two test sessions for a given S. During each test session six presentation levels were employed. These were arranged in a progression of ascending intensities in order to keep the effects of familiarity with the test vocabulary at a minimum. The total range was from -4 db to 40 db sensation level. All three types of Ss yielded articulation functions which were characterized by a linear segment at low presentation levels and a curvilinear segment at high levels. In the linear portion of the function for the normal and conductive groups the articulation score increased ac the race of 6% per decibel increase in signal intensity. In the sensori-neural group the slope of the linear segment of the function was only 3% per decibel. For all three groups, List I yielded slightly higher discrimination scores than List 11. In addition, a small improvement in discrimination scores was found from test to retest. This was true for all groups and both lists. However, in all groups, scores between lists as well as those from test to retest showed relatively high positive Pearson product-momenc correlations. The general conclusions are that: (1) Lists I and I1 are sufficiently interdependent to be considered as alternate forms of a single exploratory tool; (2) the tool itself appears sufficiently reliable to be viewed as a particularly promising method for determining the slope of the linear portion of an individual's articulation function.