To examine whether a lymphoid leukosis (LL) cell line releases an LL-specific avian leukosis virus (ALV) or not, two viral materials, culture fluid and a concentrated viral material from an LL-cell line, were inoculated into a total of 74 day-old chicks of line 15I in 5 experiments. Spectrum of diseases induced, their incidence and incubation periods to onset were examined. Fifteen chicks were inoculated with the culture fluid and 9 (60%) developed ascites [59-119 days post inoculation (dpi); geometric mean (GM) of dpi, GM: 89.6)], but LL was not induced in any chicks inoculated. Fifty-nine chicks were inoculated with the concentrated viral material and LL was recognized in 13 (22.0%) (27-74 dpi; GM: 48.4), ascites with LL in 11 (18.6%) (34-75 dpi; GM: 41.3), ascites alone in 21 (35.6%) (32-83 dpi; GM: 48.2), erythroblastosis in 2 (3.4%) (70-102 dpi; GM: 84.5), and other diseases in 12 (20.3%) (43-102 dpi; GM: 61.8). LL lesions were frequently observed in the liver, spleen, kidneys, bursa of Fabricius (bursa), bone marrow and gonads. Mild lymphocytic foci in some visceral organs and perivascular cuffing in the central nervous system were observed mainly in several chicks diagnosed as having complication of ascites with LL or other diseases. In addition to these lesions, atrophy of bursa and thymuses was recognized in them. No antibodies against Marek's disease virus (MDV) and reticuloendotheliosis virus were detected in 36 sera taken from the chicks inoculated with the concentrated viral material. Serotype 2 MDV was isolated from the buffy coat of some inoculated chicks. These results suggest that the properties of ALV inoculated and immunosuppression caused by inoculation with high doses of ALV are involved in rapid induction of LL and expression of pathogenicity of serotype 2 MDV released from the LL cell line and included in the viral inoculum. This is the first report describing the rapid induction of LL and ascites in chicks.