The growth rate and interlamellar spacing of pearlite were determined as a function of trans formation temperature at one atmosphere and 30 kilobars pressure in eutectoid iron-carbon alloys containing approximately one percent manganese. The atmospheric-pressure growth rates, measured at four temperatures in the range 560 to 680 C, were in fair agreement with data obtained on a similar alloy by other investigators. Indications were found of a change in slope of the reciprocal spacing vs temperature curve at one atmosphere corresponding to the onset of partitioning of manganese between ferrite and cementite at 640 C. High-pressure runs were made at seven tempera tures in the range 400 to 620 C. In comparison with the properties of the transformation at one atmosphere, the specimens transformed at 30 kb exhibited a decrease in pearlite growth rates by factors of up to a thousand. A substantial in crease in the interlamellar spacing of the pearlite. The results for the effect of pres sure on pearlite growth rate and spacing con firm those obtained at a single temperature in a preliminary survey made earlier in this laboratory.