Temporal changes in B19 IgG antibody in 33 BMT patients with no evidence of recent B19 infection. Group A, seronegative recipients with seronegative donors; group B, seronegative recipients with seropositive donors; group C, seropositive recipients with seronegative donors; group D, seropositive recipients with seropositive donors. (Data on patients D13 through D17 were omitted for clarity because they would have superimposed on the data for the 12 patients shown that give an accurate representation of the range of results.) The dotted line gives the manufacturer's cutoff.