The impact of differences in level of baseline responding on contingency learning in the first year was examined by considering the response acquisition of infants classified into baseline response quartiles. Whereas the three lower baseline groups showed the predicted increment in responding to a contingency, the highest baseline responders did not. Instead, they responded less in the contingency period relative to baseline. In extinction, the four baseline quartile groups failed to differ. The findings are considered in the context of the law of initial value, and some potential reasons for the effect of baseline responding on contingency learning are discussed. These studies show that variability in baseline responding may compromise our understanding of contingency detection especially for infants with high baseline response levels.