The high-resolution infrared spectra of the low-lying nu4 and nu5 fundamentals of the transient molecule formyl chloride, HCOCl, are reported. Both thype A/B hybrid bands have been analyzed in detail, providing rotational assignments for the HCO Cl-35 and HCO Cl-37 isotopomers. The excited state rotational and centrifugal distortion constants have been determined by fitting assignments over a wide range of J and K(a) values. No perturbations were detected in either band. (C) 1991 Academic Pess, Inc.