This study was purposed to investigate immune reconstitution at 12 months after allogeneic peripheral blood stem cell transplantation (all-PBSCT) and its relation with the influencing factors such as age, HLA compatibility, graft versus host disease and viral infection. The T lymphocyte subgroups (CD3(+), CD4(+), CD8(+)), B lymphocyte (CD19(+)) and NK (CD16(+)CD56(+)) cells in peripheral blood and serum immunoglobulin concentrations (IgG, IgA and IgM) of 37 patients were analyzed by flow cytometry and scatter turbidimetry, respectively at 1, 3, 6 and 12 months after transplantation. The results showed that CD3(+) cell percentage was (47.5 +/- 23.2)% at 1 month, (75.1 +/- 6.4)% at 3 months, (69.7 +/- 12)% at 6 months and (71.7 +/- 4.2)% at 12 months. CD4(+) cell percentage was (13.3 +/- 6.4)% at 1 month, (20.2 +/- 11.4)% at 3 months, (46.9 +/- 10.3)% at 6 months and (29.1 +/- 18.7)% at 12 months. CD8(+) cell percentage was (43.1 +/- 23.2)% at 1 month, (42.6 +/- 16.9)% at 3 months, (69.7 +/- 12)% at 6 months and (47 +/- 5.6)% at 12 months. CD16(+)56(+) cell percentage was (14.4 +/- 8.4)% at 1 month, (15.9 +/- 7.6)% at 3 months, (14.7 +/- 6.6)% at 6 months and (13.6 +/- 3.4)% at 12 months. CD19(+) cell percentage was (6.4 +/- 5.6)% at 1 month, (11.7 +/- 2.4)% at 3 months, (13.3 +/- 7.3)% at 6 months and (16.7 +/- 5.7)% at 12 months. The serum concentration of IgA was (0.37 +/- 0.14) g/L at 1 month, (0.28 +/- 0.21) g/L at 3 months, (0.42 +/- 0.18) g/L at 6 months and (0.53 +/- 0.34) g/L at 12 months. The serum concentration of IgG was (12.7 +/- 3.8) g/L at 1 month, (16.3 +/- 5.2) g/L at 3 months, (14.3 +/- 6.2) g/L at 6 months and (15.4 +/- 6.9) g/L at 12 months. The serum concentration of IgM was (0.56 +/- 0.24) g/L at 1 month, (0.64 +/- 0.16) g/L at 3 months, (1.1 +/- 0.35) g/L at 6 months and (1.2 +/- 0.28) g/L at 12 months. There were no significant differences between percentage of T lymphocyte subgroups in peripheral blood and serum immunoglobulin concentrations of the patients > or = 45 years old and the patients < 45 years old. The CD19(+) cell percentage of the patients with chronic GVHD at 12 month was less than that of the other ones at 12 months after transplantation. CD4(+) and CD19(+) cell percentage recovery in the patients of haploidentical transplantation was later than that in patients of HLA complete identical transplantation. The CD4(+)/CD8(+) cell ratio and CD4(+) cell percentage of those patients infected with herpes zoster were significantly lower than those without herpes zoster. It is concluded that the CD3(+) cell percentage begins to recover at 3 months after allo-PBSCT. CD4(+) cell percentage begins to recover at 6 months after allo-PBSCT. CD8(+) cell percentage begins to recover at 1 month after allo-PBSCT. B cell percentage recovers at 3 to 6 months after allo-PBSCT. NK cell percentage recovers at 1 to 3 months after allo-PBSCT. The serum concentration of IgG recovers to normal at 1 month after transplantation which is associated with routine infusion of immunoglobulin. The concentration of IgM gradually recovers to normal at 3 months after transplantation. The concentration of IgA does not recover to normal at 12 months after transplantation. The function of B cells recovers slowly in patients with cGVHD. The CD4(+) cell absolute value and CD4(+)/CD8(+) ratio significantly decrease in patients with herpes zoster.