A method for analyzing planar sample is provided. In some cases the method comprises: (a) incubating the planar sample with a capture agent that is linked to an oligonucleotide, wherein the capture agent specifically binds to complementary sites in the planar sample; (b) reading a fluorescent signal caused by extension of a primer that is hybridized to the oligonucleotide, using fluorescence microscopy. Several implementations of the method, and multiplexed versions of the same, are also provided.