A randomized trial was conducted to assess the effect of leaving heparin locks in place longer than 72 hours. Three hundred and one patients were randomly assigned to one of two groups. Group A had the lock changed every 72 hours and Group B had the lock left in place up to 168 hours. Due to withdrawals following randomization, Group A contained 116 subjects and Group B 140 subjects. No significant differences were found between the two groups in relation to age, sex, medical condition, drugs used, entries into the lock, minor complications, or incidence of phlebitis. The findings suggest that consideration could be given to extending insertion time up to 96 hours and possibly up to 118 hours.