Four-stranded G-quadruplexes consists of tracks of guanines that are stabilized by Hoogsteen base pairing. The formation of G-quadruplexes in genomic DNA contribute to numerous biological processes in vivo, including replication, transcription, and telomere maintenance. Here, we present a detailed method to detect the colocalization of G-quadruplexes with telomeres in vivo, using the BG4 antibody developed from Dr. Shankar Balasubramanian's lab.