The proto-oncogenes have the capacity for conversion to an oncogene that is capable of inducing or maintaining the transformed state when they are overly expressed or altered by mutation or rearrangement. To study the possible involvement of these genes in the neoplastic transformation of B-cell malignancies, we have analyzed their expression in 18 fresh samples obtained from the peripheral blood of patients with a variety of B-cell malignancies. C-myc (2.3 kb) and c-raf(3.8 kb) were expressed in all samples including normal lymphocytes without significant variation in the level of expression. C-fos (2.2 kb) was expressed in 13 samples and normal lymphocytes with a wide range in the level of expression. C-h-ras (2.9 kb, 1.4 kb) was expressed at a low .level in 11 and 12 samples, but not in norrnai Ivmphocytes. C-myb (3.7 kb) and c-fes (2.7 kb) were expressed at a low level in 5 and 10 wimples, respectively, including normal lymphocytes. C-sis (4.0 kb) was not detected in any sample including iwrmal lymphocytes. Our study indicates that certain oncogenes are expressed in different patterns in the various types of B-cell malignancies which suggest biological heterogeneity of B-cell malignancies at t.he malecular level.