A theoretical analysis at the ROB3LYP/3-21G* level of theory of the condensed Fukui function (f(k)) applied to a set of eight cobalt macrocycles derived of the porphyrine is performed. Two approximations for f(k) are used, finite difference (fd) and frozen core (fc), and the f(k)(-) and f(k)(+) indices are evaluated for determining the most probable reaction site for the attack of an electrophile and of a nucleophile, respectively. We found a good agreement between fd and fc calculated for f(k)(+), in the sense that both predict that the cobalt atom is the preferred reaction site receiving an electrophile. In the case of a nucleophilic attack, the comparison between the fd and fc approximations shows that both predict the cobalt atom as the most probable reaction site receiving a nucleophile. We conclude that realistic (fd) as approximate (fc) estimates of the condensed Fukui function used here in general can work very well in diagnosing reactivity trends in cobalt porphyrine and derivatives.