Blood samples are being collected to determine the variability in the development of depressive symptoms induced by interferon. Thus, we plan to measure specific genetic polymorphisms [i.e., in the serotonin (5-HT) transporter gene-linked polymorphic region (5-HTTLPR), in the promoter of the 5-HT1A receptor subtype, and an intronic tryptophan hydroxylase polymorphism]. Tryptophan, 5-HT, and cortisol blood levels will also be measured.