Background: Calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) has been extensively studied and characterized in normal mammalian tissues; however very little is known about this enzyme in human brain tumors. It has been established that high levels of this enzyme exist in non-central nervous system tumors, PDE inhibitors or cAMP analogues have been used to treat them. This study has examined the levels of CaMPDE in glioblastoma multiforme from six patients and has compared these to the levels of CaMPDE in four patients with normal cerebral tissue. In addition, an enzyme immune assay method (EIA) was developed in this study for the detection of CaMPDE in human cerebral tissue. This method is proposed to be used as an adjunct to the spectrophotometric method presently utilized. This would be beneficial in cases where small tissue samples, for example in stereotactic biopsy, are available. Methods: The CaMPDE activity and corresponding levels of expression in cerebral tissue from temporal lobectomies and both surgical extraction or stereotactic biopsy in patients with primary tumors were determined by spectophotometric and EIA, respectively. The EIA was developed from the production of a polyclonal antibody against bovine brain 60 kDa CaMPDE isozyme. Cross reactivity of the antibody with human was confirmed using transblot and immunohistochemistry. Results: Utilising the EIA, there was found to be significant reduction in both catalytic activity (p < 0.001) and in quantitative protein expression (p < 0.001) in glioblastoma multiforme from patients when compared to normal cerebral cortex. Immunoblotting experiments and immunohistochemistry demonstrated that CaMPDE in glioblastoma multiforme failed to react with a polyclonal antibody raised against bovine brain 60 kDa CaMPDE isozyme, whereas the enzyme from normal tissue reacted with antibody. Conclusions: Contrary to other studies on non-CNS tumors, the catalytic activity and the protein expression of CaMPDE is reduced in glioblastoma multiforme. The EIA method is a more sensitive in detecting CaMPDE than in the spectrophotometric method, especially when a small amount of tissue is available. Immunohistochemistry and the EIA may be useful in the future to use as markers for other types of brain tumors and not for glioblastoma multiforme as demonstrated.