OBJECTIVES To determine the response to small repeated variations in X-ray exposure of storage phosphor (SP) plates compared with Ektaspeed Plus dental film. METHODS Exposure of SP plates and Ektaspeed Plus dental film was varied within a small range [8.62 microC kg-1 to 9.03 microC kg-1, (5%)]. Radiographs were digitized and SP plates read with a laser-based scanner. Nested analysis of variance, analysis of covariance, and regression analysis were used to test the relationship between exposure and the resulting signal. RESULTS The relationship between exposure and signal for digital images of film radiographs was not significant whereas the corresponding relationship for SP images was highly significant (P < 0.001, R2 = 0.44). CONCLUSIONS Over the narrow range of X-ray exposures studied there was a significant direct linear relationship between exposure and digital gray-scale values for SP images but not for digital images of Ektaspeed Plus films.