The formyl radical (HCO) was detected in four molecular clouds as reported in 1976 by Snyder et al. It was observed toward the giant molecular clouds W3, W51, K3-50, and NGC 2024 (the Flame nebula). A follow-up study in 1985 reported observations of four additional lines beyond the single line of the original report. A 2002 paper by García-Burillo et al. found HCO to be widespread in the galaxy M82 (picture here), a starburst galaxy undergoing a massive amount of star formation. The HCO observations appear to show that the nucleus of M82 is an enormous photon-dominated region. The formyl radical was also observed in Comet IRAS-Araki-Alcock (1983d).

HCO is a precursor to formaldehyde (H₂CO). One possible pathway to the formation of both HCO and H₂CO is via addition of H to CO in icy grain mantles, though the energetics suggest that this may not be a very efficient reaction.