We determined that changes in intracellular Ca2+ concentration ([Ca2+]i) occur in human fibroblasts within the first hour of human cytomegalovirus (HCMV) infection when viral adsorption and fusion take place, and we investigated whether such changes also occur in response to monoclonal anti-idiotype antibodies (MAb2) that mimic HCMV gp86 and bind to a 92.5-kDa putative cell membrane receptor for gp86. Digitized image analysis of fura 2-loaded human embryonic lung fibroblasts indicated specific transient increases in [Ca2+]i beginning in some cells within the first 5 min of incubation with cross-linked MAb2 (70-750 nM, P < 0.01), which were similar in timing and intracellular distribution to those induced by HCMV. A primary source of Ca2+ appeared to be intracellular Ca2+ stores, since prior depletion of these stores with 30 nM thapsigargin inhibited the response (91.7 +/- 8.6%, P < 0.01); influx of Ca2+ from the extracellular medium was apparently necessary to maintain the intracellular Ca2+ stores. Transient increases in inositol trisphosphate (IP3) occurred in response to MAb2 (up to 3,329 +/- 84%, P < 0.001) or HCMV (92.8 +/- 19%, P < 0.01) during this same time period. These data suggest that the 92.5-kDa receptor for HCMV gp86 mediates an increase in IP3 and subsequent release of Ca2+ from intracellular stores.