An on-line, automated system, voltage-controlled oscillator (VCO), with digital print-out of uterine activity units (UAU) at designated intervals, has been used in clinical studies and appears reliable. A comparison was made between the VCO system and a microprocessor-controlled digital integrator system (MCDI), which displays UAUs as a bar graph every 10 minutes on the uterine activity channel of the clinical fetal monitor.