Data collection and processing. At the beginning of the study a questionnaire about the housing characteristics and possession of household goods was applied to the mother or child caretaker in all households. Hemoglobin concentrations were determined at baseline and 6 and 12 months after in capillary blood samples obtained by finger prick using a Portable Photometer Hemocue (HemoCue, Angelholm, Sweden)17, 18. Reliability of the photometers was assessed during fieldwork at the beginning and at the end of each working day. A three-level liquid quality control check (4C-ESControl, Beckman-Coulter, Miami Fla, USA), and the readings of a precalibrated reference cuvette included with the equipment were used for such purpose. The mean difference between duplicates was 0.3 ± 9.9 g/L, (P=0.36 for liquid quality control material and -0.24 ± 3.6 g/L, P= 0.27 for the reference cuvette). Venous blood samples were drawn from children at baseline and 6 and 12 mo after. Samples were centrifuged and serum was stored in color coded cryovials kept in liquid nitrogen until delivery to a central laboratory. Commercial kits were used to measure the SF concentrations, (Dade Behring Inc, Newark, DE 19714, U.S.A.) and sTfR (Dade Behring, Maburg, Germany) by ELISA. C reactive protein (CPR) was determined by nephelometry, using monoclonal antibodies (Behring Nephelometer 100 Analyzer, Behring Laboratories, Messer Grisheim Gmbh,Frankfurt, Germany. Serun zinc concentrations were mesured by Atomic Absorption spectrometry by a Analyst 300 model with graphite furnace(Perkin Elmer).