A preliminary investigation has been made of the influence of oil holes and grooves on journal bearing performance to provide, in addition to fundamental information on fluid films in bearings, preliminary data for an ultimate analysis of the behaviour of internal combustion engine bearings. In the first part of the paper the effects of supplying oil to holes and grooves in the unloaded part of the bearing are investigated, the quantity of oil flowing through the bearing, the running temperature and the coefficient of friction being recorded. Amongst the results are shown the important part the clearance space at the point of supply plays in the quantity delivered; the surprising drop of feed as a 90 deg. circumferential groove is extended to 360 deg.; the marked effect of quantity of oil on bearing temperature for small flows and the rapid drop in efficiency of oil cooling as the quantity rises; and the absence of a groove arrangement giving more efficient cooling than the others. Change of supply temperature and pressure have a much less than proportionate effect on bearing temperature and flow. Increase of clearance leads to a disproportionate increase of oil flow. In the second part of the paper the effect of holes and grooves in the pressure film is explored. In this case measurements were made of the pressure at the crown of the bush when the hole there was closed, and of the flow when open, in addition to the previous observations. Amongst the results may be noted the relatively small initial flow through the crown hole in spite of the high pressure there when it is closed; the increase of the crown hole flow at the expense of side flow as the groove is cut into the inlet film; and the relatively small changes in bearing temperature and coefficient of friction. Again changes of oil supply pressure and temperature had less than proportionate effects on flow and temperature of the bearing. A preliminary note is made of the decrease of load-line film pressure which was found as the temperature was increased. The temperature was also raised to cause incipient failure of the bush, and it was found that the final temperature was independent of whether the crown hole was open or closed, and yet there were indications of diminished film thickness for small grooves at natural running temperatures. The safety was decreased as grooves were cut in the loaded part of the bearing; some indications of the magnitudes of the changes are given.