Thirty-nine C4 to C6 motor complete Frankel A or B spinal cord injured subjects were included in this prospective study to determine the course of recovery in the zone of partial preservation (ZPP) during the first 6 months postinjury. Subjects had initial manual muscle testing and neurologic examination between 3 and 7 days postinjury. Subjects whose most rostral key muscle in the ZPP had a motor power of grade 1 or 1+/5 (group 1, n = 22) were compared with subjects whose most rostral key muscle had a motor power of grade 2 or 2+/5 (group 2, n = 17). Subjects had manual muscle testing weekly for 1 month and then monthly for 6 months postinjury. Comparisons were made for recovery to: (1) grade 3/5; (2) grade 4/5; (3) an increase of one grade; and (4) an increase of two grades. Analyses were made at monthly intervals by the Fisher Exact test and between median times of recovery by the Kruskal-Wallis Ranking test. There was earlier recovery to grade 3/5 for group 2. At one month 11 of 17 (65%) group 2 subjects had reached grade 3/5 compared with 4 of 22 (18%) group 1 subjects (p less than 0.01). At 2 months postinjury, 14 of 17 (82%) group 2 subjects versus 10 of 22 (45%) group 1 subjects had reached grade 3/5 strength (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)