The protection period of a 200,000 IU of vitamin A on Filipino children was determined. Subjects were 105 children aged 1-5 years given a single massive dose during the "Araw ng Sangkap Pinoy" (ASAP) in March 1995. Serum retinol was measured by HPLC at baseline, one, two, four and six months after the administration of the dose. Results showed that baseline serum retinol levels were significantly lower than all follow-up values. Serum retinol values were maintained at levels higher than pre-supplementation values although the values decreased on the second month after supplementation. The proportions of deficient and low (< 20 microg/dl) levels were significantly lower one and six months after supplementation. All follow-up serum retinol levels of children with deficient and low values at baseline were significantly lower (p < 0.001) than those with normal values. The WHO recommendation of 200,000 IU was effective in increasing serum retinol concentrations and maintaining it above pre-supplementation levels up to 6 months after administration of the dose. It also replenished organic vitamin A reserves as shown by the dose response (S30DR) approach. Incidence of infection also decreased among the children. Supplementation with vitamin A has likewise resulted in an increase in hemoglobin values and a decrease in the proportion of anemics (Hb < 11.0 g/dl) among the children.