Detection of provirus sequences by in situ PCR amplification. Peritoneal granulocytes and macrophages were obtained 24 and 96 hours, respectively, after thioglycollate injection from control (A and C) or from mice reconstituted with targeted spleen cells (B and D) 12 months earlier and subjected to in situ PCR hybridization using biotinylated probes. Amplified neo-specific sequences were visualized on a cell per cell basis using an alkaline phosphatase-based colorimetric assay.