We studied the relationship between changes in auditory brainstem responses (ABR) and serum and cerebrospinal fluid levels of neuron-specific enolase (NSE) in hyperbilirubinemic 2- to 8-d-old piglets. Infusion of a stabilized solution of bilirubin resulted in serum bilirubin levels of 571.1 +/- 48.8 mumol/L (mean +/- SEM) after 6 h. ABR were obtained at baseline and then hourly until the piglets were killed. We measured peak amplitudes and latencies for waves I-V, as well as latency for the post-V trough. Changes in amplitudes and latencies were analyzed as slopes because of heterogeneous variances. Over time, a significant reduction was observed in peak II-V amplitudes of bilirubin-infused piglets, but not in those of corresponding controls. No change was observed in latencies. NSE was analyzed by RIA. Serum NSE remained stable throughout the experiment (means 5.1-6.6 micrograms/L) and did not differ between the groups. Cerebrospinal fluid NSE values also remained stable, and no differences that could be ascribed to hyperbilirubinemia were detected. We conclude that hyperbilirubinemia induced significant changes in piglet ABR amplitudes without concomitant evidence of severe neuronal compromise, as might have been indicated by significant increases in serum and/or cerebrospinal fluid NSE levels. This provides further support to the clinical impression that early ABR changes during hyperbilirubinemia may be reversible.