We have investigated the biological fluids--serum, cerebrospinal fluid, and urine--of three strains of rats; the present data extend our database (also available on-line) and may be of interest for pharmacological and toxicological investigation. Specifically, we have defined reference maps of the major protein components in cerebrospinal fluid and urine. Compartment-specific isoforms were recognized for transferrin and transthyretin. Mass spectrometric data established the cleavage site of the signal peptide and identified the N-terminal blocking group of prostaglandin D synthase from rat cerebrospinal fluid. A previously undescribed member of the family of low molecular mass rat urinary proteins was characterized as containing a sequence similar, but not identical, to the N-terminal region of rat urinary protein-2 (RUP-2), and divergent from RUP-1.