The objective of this study was to test the validity of the so-called total end range time (TERT) theory. This theory claims that the amount of increase in passive range of motion (PROM) of a stiff joint is proportional to the amount of time the joint is held at its end range, or total end range time. Proximal interphalangeal joint (PIP) flexion contractures were chosen as a model upon which to test the theory. Digital extension casts were used to hold the PIPs at the end range of extension. Fifteen patients with 20 PIP flexion contractures between 15 degrees and 60 degrees volunteered for this study. All contractures resulted from primary orthopedic conditions; none arose from a central nervous system lesion. Each joint was treated by two periods of continuous casting in extension: a 6-day period and a 3-day period. Patients were randomly assigned to one of two groups. Group A subjects wore the initial casts for 6 days and the subsequent casts for 3 days. Group B subjects wore the initial casts for 3 days and the subsequent casts for 6 days. Passive range of motion changes were measured under a controlled torque PROM technique before and after each casting period. The sum of the gains in PROM for all subjects during their 6 days of casting totaled 106 degrees (chi = 5.3 degrees). The total gain during the 3 days of casting was 60 degrees (chi = 3.0 degrees). This finding was significant at the p < 0.005 level of confidence.(ABSTRACT TRUNCATED AT 250 WORDS)