We demonstrate the use of a camera phone as a low-cost optical detector for quantitative analysis of a high-sensitivity C-reactive protein (hs-CRP) enzyme-linked immunosorbent assay (ELISA). The camera phone was used to acquire images of the ELISA carried out in a conventional 96 well plate. Colorimetric analysis of the images was used to determine a standard curve that exhibited excellent agreement with a fitted 4-parameter logistic model (R²=0.998). The limit of detection (LOD) for this approach was determined to be 0.026 ± 0.002 μg/ml (1.035 ± 0.079 μM) CRP. Furthermore, these results were found to be in very close agreement with measurements obtained for the same assay using a laboratory-based instrument. These findings indicate the basic technology to enable low-cost quantitative home-based monitoring of an important clinical biomarker of inflammatory disease may already be present in the patient's home.