Rats were trained to discriminate 8 seconds duration under a differential reinforcement of long latencies (DRLL) schedule. Once the discrimination was learned, rats were implanted with an indwelling vascular catheter in femoral artery. A femoral arterial catheter (PE20 heat-fused to PE10) was inserted into a rat for measurement of blood pressure. The catheter was routed subcutaneously to exit at the back of the neck and connected to syringe with extension tubing (PE50 heat-fused to PE20). The vascular catheter was flushed with saline containing heparin, and the rats were placed in individual Plexiglas home cages. After recovery of surgery, blood pressure and response latencies were recorded on a DRLL8' schedule in a operant chamber. Arterial pressure was slightly changed with the time stages on a DRLL8' schedule. Arterial pressure was elevated for the end of a eight seconds trial. The results showed that temporal discrimination correlated with internal cardiovascular changes. The femoral artery catheterization procedure is preferable in terms of simultaneously recording of blood pressure and response latencies.