This was a random-order, double blind cross-over trial of 2 formulations of a ready-to-use supplementary food (RUSF), one fortified with arginine and citrulline and provided with a daily anti-inflammatory dose of chloroquine (RUSF-v) and a basic formulation (RUSF-b) provided with a standard anti-malarial prophylactic weekly dose of chloroquine. The study was designed to test the hypotheses: (1) supplementary arginine, citrulline and daily chloroquine increases bioavailable arginine and flow-mediated-dilatation (FMDmax%; a measure of NO-dependent endothelial function), and (2); protein energy supplementation in the form of RUSF improves nutritional status in children with sickle cell disease.