The interactions of hydrophobically modified poly(acrylamide) (HMPAM) and unmodified poly(acrylamide) (PAM) with sodium dodecyl sulfate (SDS) or tetradecyltrimethylammonium bromide (TTAB) have been studied by flow microcalorimetry at 302.7 K. The mixing enthalpy curves were determined by mixing SDS and TTAB solutions above their critical micelle concentration with HMPAM or PAM solutions of different concentrations. The mixing enthalpy curves of SDS and TTAB solutions with water were also determined. The critical aggregation concentrations (cac) and the thermodynamic parameters have been derived from the differential enthalpy curves. Pronounced endothermic peaks were detected for all the systems. The peak heights of the endothermic curves decrease with increasing hydrophobicity of the HMPAM samples. The HMPAM hydrophobicity has no obvious effect on the values of the cac. The interaction between TTAB and the polymers is much weaker than that between SDS and the polymers.