This paper provides a direct approach to obtaining formulas for deriva
tives of functionals of point processes in rare perturbation analysis
([2], [6]). Results are obtained for arbitrary (not necessarily statio
nary) point processes in R and R(d), d greater than or equal to 2, und
er transparent conditions, close to minimal. Formulas for higher-order
derivatives allow one to construct asymptotical expansions. The resul
ts can be useful in sensitivity analysis, in light traffic theory for
queues and for computation by simulation of derivatives at positive in
tensity, while the computation of the derivatives via statistical esti
mation of the functional itself and its increments usually gives poor
results.