Pharmacokinetics of HA22-LR. Balb/c mice were injected intravenously with 10 μg of either HA22 (□) or HA22-LR (○) and bled at several intervals between 2 and 60 minutes from the time of injection. The concentration of immunotoxin in the serum at the various intervals was determined by ELISA and fit to a single exponential decay function. The corresponding half-life (t_1/2) is indicated. Each point is the concentration of immunotoxin in the serum of one mouse, and the concentration at each time interval was determined from at least 2 different mice.