  Recently a general growth curve including the well known growth equations,
such as Malthus, logistic, Bertallanfy, Gompertz, has been studied. We now
propose two stochastic formulations of this growth equation. They are obtained
starting from a suitable parametrization of the deterministic model, by adding
an additive and multiplicative noise respectively. For these processes we focus
attention on the First Passage Time from a barrier and on the First Exit Time
from a region delimited by two barriers. We consider thresholds, generally time
dependent, for which there exist closed-forms of the probability densities of
the first passage time and of the first exit time.
