[en] Susceptibility to cytostatic activity of non-activated macrophages (Mph) of Syrian hamster embryo fibroblasts (HEF) transformed in vitro by BAV-3, SV40, RSV-SR, or spontaneously and of their in vivo selected variants was studied in dynamics (5 days of co-incubation). With the use of ³H-TdR incorporation test it was demonstrated that HEF transformed by BAV-3 appeared to be able to overcome the cytostasis at co-incubation with with Mph, in contrast to deeply suppressed spontaneously transformed cells of STHE strain. HEF transformed by SV40, or RSV-SR appeared to be resistant to growth-inhibiting activity o Mph during almost all the 5-day period. The in vivo selected malignant variants of STHE cells were able to recover from cytostasis after 4-5 days of the co-incubation with non-activated Mph, in contrast to low-malignant variant and to parental cell strain. (author)