The involvement of 124 young mothers in a doula support program was measured in two dimensions--quantity of program contact and quality of mother-doula helping relationship. The study examined each dimension's differential associations with maternal outcomes, as well as the moderating effects of mother characteristics on these associations. Quantity of program contact was related to the quality of helping relationship, especially when rated by doulas. Both quantity and quality of involvement predicted the maternal outcomes, although not always in the expected direction. For mothers with limited vocabulary skills and better connections with the baby's father, program contact was more likely to promote positive birth experiences. A negative association between program contact and parenting behaviors was observed among mothers who were less mature or had less positive social relationships. The study suggests the multidimensionality of program involvement and the complexity of interactions between program and participant factors in producing program outcomes. (Contains 4 tables, 1 figure and 2 footnotes.)