One hundred and six HIV-positive drug users were tested with a two-tone auditory evoked potential (AEP) task and a small battery of neuropsychological tests, to examine the relationship between the latency of the P300 component (P3) of the AEP, intellectual function, mood and drug use. Principal components analysis revealed a significant correlation between P3 latency and the first principal component (r = -0.43, P < 0.001). Varimax rotation generated three orthogonal components which we interpreted as intellectual performance, memory, and mood. Intellectual performance and self-reported mood were individually correlated with P3 latency, but memory was not (r = -0.36, P < 0.001; r = 0.23, P < 0.05; and r = -0.18, NS, respectively). Subjects with symptomatic HIV disease had a higher correlation between P3 latency and intellectual performance than subjects with asymptomatic HIV disease and, among patients with symptomatic HIV disease, poorer memory was associated with a lower CD4 count. Opiate or benzodiazepine consumption did not correlate with poor intellectual performance, memory, or self-rated mood in our sample. These results indicate that there is a relationship between AEP latency and neuropsychological measures of intellectual function, and that it is influenced by subjective mood. Surprisingly, declared current drug use has no discriminable effect on these relationships.