Measurements have been made of chloro-iodomethane (CH2ClI) in seawater samples collected in the N.W. Atlantic. Elevated concentrations (>3 ng/L) were found in surface waters at a number of locations in the pelagic zone. Background surface concentrations in the pelagic zone were 0.1--0.4 ng/L. Coastal/shelf regions averaged 0.1 ng/L off Labrador and Greenland, and 0.8 ng/L on the Grand Banks. We suggest that its distribution may be due to a phytoplankton source, either direct or indirect (i.e., via an intermediate compound). Using measurements of methyl iodide (CH3I made on the same samples, we make a first order estimate of the comparative fluxes of the two compounds from ocean to atmosphere. This indicates that the iodine carried by CH2ClI may be comparable with that carried as CH3I. Refinement of the flux estimates requires measurements of atmospheric concentrations of CH2ClI, and determination of its Henry's Law constant. ¿ American Geophysical Union 1992