An essential prerequisite for the accurate interpretation of noninvasive functional brain imaging techniques, such as blood oxygen level dependent (BOLD) fMRI, is a thorough understanding of the coupling relationship between neural activity and the haemodynamic response. The current study investigates this relationship using rat barrel cortex as a model. Neural input was measured by applying current source density (CSD) analysis to multi-laminar field potentials to remove ambiguities regarding the origin of the signal inherent in single electrode recordings. Changes in cerebral blood flow (CBF) were recorded with a laser Doppler flowmetry probe. The magnitude of neural and CBF responses were modulated over a large range by altering both the intensity and frequency of electrical whisker pad stimulation. Consistent with previous findings [Devor, A., et al., 2003. Neuron 39, 353-359; Sheth, S.A., et al., 2004. Neuron 42, 347-355] a power law function well described the relationship between neural activity and haemodynamics. Despite the nonlinearity of the coupling over the whole data set, the relationship was very well approximated by a linear function over mid-range stimuli. Altering the frequency of stimulation at 1.2 mA shifted the neural activity and corresponding haemodynamic response along this linear region, reconciling recent reports of a nonlinear relationship [Devor, A., et al., 2003. Neuron 39, 353-359; Jones, M., et al., 2004. NeuroImage 22, 956-965; Sheth, S.A., et al., 2004. Neuron 42, 347-355] with previous work that found a linear coupling relationship when altering stimulation frequency [Martindale, J., et al., 2003. J. Cereb. Blood Flow Metab. 23, 546-555; Ngai, A.C., et al., 1999. Brain Res. 837, 221-228; Sheth, S., et al., 2003. NeuroImage 19, 884-894]. Using stimuli within this linear range in imaging studies would simplify the interpretation of findings.