Bioassays showed that in-transit fumigation of corn in the holds of a bulk dry-cargo vessel with phosphine or with the liquid fumigant 80-20 were effective against stored-grain insects wherever adequate concentrations of fumigant were achieved and sustained. Although distribution of both fumigant gases was nonuniform, no exposed insects survived the fumigation with phosphine. In contrast, some insects on the surface of the corn and at the sides of the holds survived the treatment with 80-20. Highest concentrations of phosphine were sustained near the surface, and phosphine was slow to reach the bottom of the holds. Also, as the concentration of phosphine decreased near the surface during aeration, it increased at the bottom of the holds. None of the fumigant gases were detected in working areas or living quarters of the ship in transit, but during unloading, low levels of phosphide were occasionally detected on the surface of the grain and in the belt house of the unloading facility. Residues of phosphine were highest on unaerated samples taken directly from the surface of the corn before unloading began, but these residues did not exceed 5.6 ppb.