Previous in vivo biotelemetry studies have demonstrated that short-term streptozotocin (STZ)-induced diabetes is associated with a reduction in heart rate (HR), heart rate variability (HRV), body temperature and prolongation of QT and QRS intervals (Howarth et al. 2005). This study investigates the long-term effects of STZ-induced diabetes on the electrocardiogram (ECG), physical activity and body temperature in rats. The transmitter devices were surgically implanted in 10 young adult male Wistar rats (220-230 g) under general anaesthesia (sodium pentobarbitone, 45 mg/kg, i.p.). Electrodes from the transmitter were arranged in Einthoven bipolar Lead II configuration. ECG, physical activity and body temperature data were continuously recorded with a telemetry system before and following the administration of STZ (60 mg/kg) for a period of 22 weeks. HR, physical activity and body temperature declined rapidly 3-5 days after the administration of STZ and the effects became more conspicuous with time reaching a new steady-state approximately 1 to 2 weeks after STZ treatment. The HR at 4 weeks was 268 ± 5 beats per minute (BPM) in diabetic rats compared to 347 ± 12 BPM in age-matched controls. The HRV at 4 weeks was also significantly reduced after STZ treatment (18 ± 3 BPM) compared to controls (33 ± 3 BPM). The HR and HRV were not additionally altered in either diabetic (266 ± 5 and 20 ± 4 BPM) or age-matched controls (316 ± 6 and 25 ± 4 BPM) at 22 weeks. Reduced physical activity and/or body temperature may partly underlie the reductions in HR and HRV. In addition the increased power spectral low frequency/high frequency ratio from 4 weeks after STZ treatment may indicate an accompanying disturbance in sympathovagal balance. Data are mean ± SEM. Statistical comparisons were made using independent sample t test or ANOVA followed by Bonferroni corrected t test for multiple comparisons, as appropriate. P values less than 0.05 were considered significant.