Defects in contraction and heart rhythm have been frequently observed in streptozotocin (STZ)-induced diabetic cardiomyopathy. A telemetry system (Data Sciences Int., USA) was used to monitor the effects of insulin treatment on heart rhythm, physical activity and body temperature in STZ-induced diabetic rats. The system comprised transmitter devices (TA11CTA-F40), receivers (RPC-1), a data exchange matrix (20CH) and a personal computer for system configuration, control and data storage. Transmitters were surgically implanted in 5 male Wistar rats (225-230g) under general anaesthesia (sodium pentobarbitone, 45 mg/kg i.p.). The transmitter devices were inserted in the peritoneal cavity and electrodes from the transmitter were arranged in Einthoven bipolar Lead II configuration. After recovery from surgery baseline data was collected for a period of 10 days. All 5 rats then received a single intraperitoneal injection of STZ (60 mg/kg bodyweight) dissolved in citrate buffer. Twenty days later rats received daily subcutaneous injections of Ultratard insulin (Novo Nordisk) for a period of 30 days; after completion of the experiments the rats were humanely killed. The dose of insulin ranged from 4-9 units per day dependent on levels of blood glucose. Biotelemetry data were recorded for 5 min of every hour, 24 h per day for the duration of the study. Statistical comparisons were made using paired t test and P values less than 0.05 were considered significant. Typical blood glucose values before STZ treatment were 63±1, and 20 days after STZ were 317±13 and during the period of insulin treatment were 64±13 and 165±12 mg/dl measured at 8 and 24 h after insulin, respectively. Heart rate (HR) during the baseline period was 361±7 b.p.m. and was significantly reduced after STZ treatment (266±12 b.p.m.). There was a significant recovery of HR towards pre-STZ levels during insulin treatment (303±14 b.p.m.). Heart rate variability (HRV) during the baseline period was 25±3 b.p.m., during STZ was 16±2 and was not significantly altered by insulin treatment (17±1 b.p.m.). Activity during the baseline period was 1.4±0.2 counts per minute (c.p.m.), after STZ was 0.8±0.2 c.p.m. and during insulin treatment was 0.9±0.1 c.p.m.. Body temperature during the baseline period was 37.5±0.1°C and was significantly reduced after STZ treatment (37.2±0.2°C). There was a significant recovery of body temperature towards pre-STZ levels during insulin treatment (37.5±0.1°C). Treatment with insulin produced a significant recovery in HR and body temperature but had little effect on HRV and physical activity in STZ-induced diabetic rats.