The presence of adrenomedullin-like immunoreactivity in the cerebrospinal fluid was studied by radioimmunoassay in 13 subjects with various neurological diseases. The concentrations of adrenomedullin-like immunoreactivity in the cerebrospinal fluid were 9.4 +/- 3.1 pmol/l (mean +/- SD, n = 13). Reverse-phase high performance liquid chromatography of the extract of the pooled cerebrospinal fluid showed that approximately 40% of the adrenomedullin-like immunoreactivity was chromatographically identical to human adrenomedullin (1-52). This is the first report that demonstrates the presence of adrenomedullin-like immunoreactivity in the human cerebrospinal fluid.