The present invention relates to neutral soluble .beta.-glucans which exert potent and specific hematopoietic and immunological effects without stimulating the production of certain cytokines, to preparations containing the novel .beta.-glucans, and to a novel manufacturing process therefor. The neutral soluble glucan preparation has a high affinity for the .beta.-glucan receptor of human mono-cytes and retains two primary biological (or immunological) activities, (1) the enhancement of microbicidal activity of phagocytic cells, and (2) monocyte and neutrophil hemopoietic activity. Unlike soluble glucans described in the prior art, the neutral soluble glucan of this invention neither induces nor primes IL-1 and TNF production in vitro and in vivo. Safe and efficacious preparations of neutral soluble glucan of the present invention can be used in therapeutic and/or prophylactic treatment regimens of humans and animals to enhance their immune response, without stimulating the production of certain biochemical mediators (e.g., IL-1, TNF and leukotrienes) that can cause detrimental side effects, such as fever and inflammation.