We report an unambiguous detection of the ¹³CCH and C¹³CH isotopomers of the ethynyl radical towards the Orion A ridge by identification of their N = 2 → 1 transitions. The observations have been made with the IRAM 30 m telescope at Pico Veleta, Spain. By these measurements, we confirm an earlier tentative detection of four hyperfine components of C¹³CH with the KOSMA 3 m telescope at Gornergrat, Switzerland. Although uncertainties in the calibration of line intensities are not completely settled, these observations suggest that C¹³CH might be the more abundant of the two ¹³C isotopomers. This tentative finding pertains towards the region where the emission of molecular radicals peaks, i.e., northeast of the Kleinmann–Low nebula. Furthermore, the N = 1 → 0 transition of C¹³CH has been detected in the same region with the SEST 15 m telescope at La Silla, Chile. In combination with the laboratory N = 4 ← 3 and N = 5 ← 4 data, we derive improved ground state rotational constants for both species.