Ten fusion proteins derived from five various CMV encoded proteins were used for the detection of specific antibody response by immunoblot technique in sera from renal transplant recipients. The fusion proteins were derived from the following CMV specific proteins: the assembly protein ppUL80a with an apparent molecular weight of 38 kD, ppUL99 (MW of 28 kD), the basic phosphoprotein ppUL32 (MW of 150 kD), the lower matrix protein ppUL83 (65 kD), and the DNA binding protein ppUL44 (MW of 52 kD). Some fragments overlapped and responses to these recombinant proteins were compared. Antibody responses appeared to be predominately directed at fusion proteins of ppUL32, the basic phosphoprotein and at ppUL44, the major DNA binding protein. Some differences were found in the responses to these partly overlapping fusion proteins. In addition, an IgM response mainly present in primary infections to fusion proteins XP1 and G2, again representing ppUL32 and ppUL44, was found.