The total protein and urea concentrations in perilymph, CSF and serum were determined following intracisternal injection of albumin and urea in cats. Total protein concentration in perilymph increased abruptly when total protein in CSF increased following injection of albumin. The total protein concentration in perilymph equalled two-thirds of the protein concentration in CSF by the first hour and remained fairly constant throughout the second and third hours although the protein concentration in CSF decreased during this time. The concentration of urea in both perilymph and serum increased as urea concentration in CSF increased. However, urea concentration in perilymph returned to the original value after 2 hours. This concentration remained constant and paralleled serum urea concentration even though the level of urea in CSF remained approximately five times higher than its initial value. The relationship between these findings and the etiological factors of clinical disorders such as antibiotic toxicity, Menibre's disease and hearing impairment after hemodialysis are discussed.