A field testing program was established in Honolulu to investigate negative skin friction and downdrag on prestressed concrete piles in underconsolidated, highly plastic silt-clay. The ability of bitumen coatings to reduce negative skin friction was also investigated The test site is located in an area which was reclaimed from the Keehi Lagoon during the 1930's and 40's. The soft clays were formed as a result of marine sedimentation and sedimentation from streams which flow into the lagoon. The clays are soft and compressible to a depth of 140 feet. The rate of ground settlement due to in situ pore pressures is about 1/2 to 3/4 inches per year (mid 1970's) Five 16-1/2 inch piles were employed in a comparative field study. Three of the piles were coated with different grades and thicknesses of bitumen to reduce downdrag while the other two piles acted as uncoated reference piles to measure the full downdrag. A 12-foot embankment was placed over the piles to accelerate the consolidation-downdrag process Pile compression data was obtained from multi-rod extensometers installed in a central hole in each pile. From this data the distribution of downdrag forces acting along each pile was established. After six months of observations the peak downdrag values on the uncoated piles were 165 and 194 tons. After 3-1/2 years the peak values were 340 and 345 tons. These values exceeded predictions based on total stress analysis (undrained strength) and effective stress analysis (Beta Method) The bitumen coatings were very effective in minimizing the development of negative skin friction. In one pile with a 3/16 inch thick coating, the increase in downdrag load in the coated length of the pile through the soft clay was nearly zero. Another pile with a 1/16 inch coating also exhibited a low rate of load increase with depth. On a third pile, a less viscous coating, 1/8 inch thick, was also effective in reducing downdrag The results from the uncoated piles exceeded the predictions of negative skin friction based on the semi-empirical Beta Method. Values of (beta) of 0.47 and 0.31 were calculated from the measured load distributions The procedure for applying bitumen and installing the piles is presented. Pertinent practical experiences with regard to the application and maintenance of the bitumen coatings are presented