An international exercise, registered as EUROMET project n° 907, was launched to measure both the activity of a solution of 124Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories. This paper presents the results of the first part of the exercise dealing with the comparison of activity measurements. In order to identify possible biases, the participants were asked to use all possible activity measurement methods available in their laboratory and then to determine their reference value for comparison. Thus measurement results were given using 4 pi beta-gamma coincidence/anti-coincidence counting, CIEMAT/NIST liquid scintillation counting, 4 pi-gamma counting with well-type ionization chambers and well-type crystal detectors. The results are compared and show a maximum discrepancy of about 1.6%, possible explanations are sought.