To characterize further the persistent pulmonary infiltrates, the PLI was measured using a modification to a method described previously [19, 20] . Because this is a routine procedure, informed consent was waived. Autologous RBCs were labeled with 99m Tc (11 MBq, physical half-life 6 hours; Mallincrodt Diagnostica, Petten, The Netherlands), using a modified in vitro method. Ten minutes after injection of the labelled RBCs, transferrin was labelled in vivo, following intravenous injection of 67 Ga-citrate (6 MBq, physical half-life 78 hours; Mallincrodt Diagnostica). Patients were in the supine position, and two scintillation detection probes were positioned over the right and left lung apices. The probe system (manufactured by Eurorad C.T.T., Strasbourg, France) consists of two small cesium iodide scintillators (15 × 15 × 15 mm 3 ), each in a 2-mm tungsten and 1-mm aluminium housing cover (35 mm in diameter and 40 mm in height). The front end of each probe has an aluminium flange attached (3 mm in thickness and 70 mm in diameter) to facilitate easy fixation to the patient's chest with tape. Each probe weighs approximately 255 g. The probe signals are led into a dual amplifier, from which the output is fed into a multichannel analyzer system connected to a personal computer. Because the probes have separate channels, there is no electronic crossover.