The purpose of this investigation was to determine the effect of experimental conditions on the concentrations of atenolol and acetaminophen in brain microdialysate, and to investigate the feasibility of performing repeated experiments within individual rats. Following intravenous bolus administration, reproducible concentration-time profiles were obtained in plasma and in brain dialysate. Based on corrections for in vitro recoveries of the intracerebral probe, the estimated ratio of the AUC in brain extracellular fluid (AUCbrain ECF) over the AUC in plasma (AUCplasma) +/- S.E.M. was 3.8 +/- 0.6% (n = 6) for atenolol and 18 +/- 2% (n = 6) for acetaminophen. Upon intracerebroventricular administration, interanimal differences in kinetics of acetaminophen in brain dialysate were observed while the concentrations of atenolol were below the detection limit of the assay. The influence of the use of isotonic versus hypotonic perfusate solutions on AUCbrain ECF values after intravenous bolus administration of both drugs was determined. Repeated experiments with the isotonic perfusate (24, 48 and 78 h post-surgery) resulted in AUCbrain ECF values with the ratio of 100: 98: 76% for acetaminophen and 100: 103: 98% for atenolol. Using a hypotonic perfusion solution the ratio of AUCbrain ECF values was 100: 154: 114% for acetaminophen and 100: 378: 427% for atenolol. A clear effect of the temperature of the hypotonic perfusate (24 vs 38 degrees C) on acetaminophen AUCbrain ECF values was revealed. The ratio of AUCbrain ECF values obtained at 24: 38 degrees C was 192: 100%.(ABSTRACT TRUNCATED AT 250 WORDS)