The Beta Canis Majoris variables 15 CMa and 1 CMa were observed photoelectrically in yellow light during the 1971/72 season. 15 CMa shows random amplkude variations at its known period of 0d.1 8 a re-discussion of earlier published photometry and radial velocities confirms this and also indicates that the period is variable, although the form of the variation cannot be determined. There may be other periodicities present, but this cannot be clearly ascertained in the data available. 1 CMa, on the other hand, with a period of od.2o96, showed a remarkably stable light curve shape during 1971/72, although earlier published photometry indicates that the curve may not always have had the same shape. The period is constant to about I s/century. 15 CMa is probably one of the least stable and ` CMa one of the most stable pulsators amongst the CMa class of variable.