The stability of the saliva/plasma (S/P) concentration ratio of atrazine was determined under varying conditions of salivary flow rate and plasma concentration of atrazine in Sprague-Dawley rats. In the salivary flow study, whole saliva samples were collected at different salivary flow rates while the plasma concentration of atrazine was maintained at a steady-state level of approximately 150 pg/L. In the plasma level study, whole saliva samples were collected at two steady-state plasma concentrations of atrazine (50 and 250 pg/L), while salivary flow rate was maintained at a relatively constant level. In both studies, atrazine concentrations in whole saliva and arterial plasma demonstrated a consistent relationship, but salivary concentrations were always lower than those of arterial plasma. Linear regression analysis demonstrated that the S/P concentration ratio of atrazine was not significantly different for salivary flow rates ranging from 23 to 92 pL/min/kg body weight, and did not vary for atrazine plasma concentrations between 30 and 433 pg/L. The S/P concentration. ratio of atrazine was relatively constant throughout each experimental period (0.68 t 0.1 and 0.70 i 0.1 1 for salivary flow and plasma level studies, respectively) and did not differ significantly between rats. When data from both studies were pooled, salivary concentrations were highly correlated with plasma concentrations (r2 = .94). It is concluded that under these experimental conditions, thy stability of the S/P concentration ratio of atrazine i s not affected by variations in salivary flow rate or atrazine plasma concentrations. The results from this study support the conclusion that atrazine salivary concentrations can be used to predict plasma levels of atrazine in rats.