The great improvement achieved in last years in the sensitivity of radioastronomical receivers is allowing nowadays to detect interstellar molecules down to unprecedented abundance levels. In this tak I will present the detection of various organic molecules in cold dense clouds. The ketenyl radical (HCCO) and protonated cyanogen (NCCNH+) have been detected for the first time in space in various dark clouds down to abundance levels as low as 1e-12-1e-11 relative to H2, while other molecules such as the HCO radical and propylene (CH2CHCH3), which were known to be present in just a few cold dense clouds, have been detected in a wide sample of such sources. I will discuss the implications of these detections for our current understanding of the chemistry of cold dense clouds.