Background: The relative-dose-response (RDR) test is used to identify subjects with marginal liver vitamin A stores, but its use has not been evaluated during episodes of infection. Objective: The objective was to assess, with the RDR test, the vitamin A status of children recovering from pneumonia. Design: As part of a double-blind, placebo-controlled clinical trial of high-dose vitamin A supplements among children hospitalized with pneumonia in Lima, Peru, we examined the association of treatment group, nutritional status, severity of disease, and induction of the acute phase response [on the basis of serum C-reactive protein (CRP)] on serum retinol and the RDR test. Results: Serum retinol was low at admission and increased significantly in both the vitamin A and placebo groups during recovery. Serum CRP had a significant, inverse association with retinol at both admission and discharge. Serum retinol and CRP concentrations never differed significantly between the treatment groups. Among subjects with CRP ≥ 10 mg/L, 21% in the vitamin A group and 20% in the placebo groups (P = 0.83) had a positive RDR test result. Among subjects with CRP < 10 mg/L, 56% in the placebo group but only 6% in the vitamin A group had positive RDR test results (P = 0.002). Conclusion: The RDR test was useful in assessing the vitamin A status of children recovering from pneumonia when CRP concentrations were < 10 mg/L but not when CRP concentrations were higher.