We used time point studies to document the progression of neoplasms, haematologic abnormalities and associated lesions induced by Moloney murine sarcoma virus-349 (MoMuSV-349). BALB/c mice inoculated intraperitoneally with MoMuSV-349 first developed histologically discernible lesions at 14 days post-inoculation (d.p.i.). The initial neoplasms were characterized by whorls of fusiform or spindle-shaped cells enmeshing dense infiltrates of neutrophils and macrophages. By 21 d.p.i., clinical signs associated with MoMuSV-349 infection were evident. The distribution of the neoplasms was more widespread, although the histologic appearance of the tumours was very similar to that found at 14 d.p.i. All mice sacrificed at 28 d.p.i. exhibited characteristic clinical signs associated with MoMuSV-349, including moderate cachexia. Histologically, neoplasms observed at 28 d.p.i. contained a significant vascular component. By 35 d.p.i., all mice exhibited severe clinical signs (e.g. cachexia, dull hair coat, uneven gait). Histologically, all the neoplasms had a predominant vascular component. Non-neoplastic lesions, such as severe thymic atrophy and multifocal pulmonary haemorrhage, were commonly present. Mice sacrificed 42 d.p.i. were clinically, grossly and histologically similar to those sacrificed at 35 d.p.i. However, one difference found in the 42 d.p.i. group was the presence of rare rhabdomyosarcomas infiltrating the skeletal muscles. Mice inoculated with MoMuSV-349 developed severe neutrophilia and lymphopenia, and moderate anaemia. This study demonstrates that MoMuSV-349 induced angiosarcomatous neoplasms are characterized by stage development and severe haematologic and non-neoplastic abnormalities.