Glucocorticoids (GCs) have many complex quantitative and qualitative immunosuppressive effects which induce cellular immunodeficiency and increase host susceptibility to various viral, bacterial, fungal and parasitic infections. As cortisol secretion is inadequate in chronic immune/inflammatory conditions, and current therapies have the aim of providing adequate (low) compensatory doses, the timing of GC administration, such as during the nocturnal turning-on phase of tumour necrosis factor (TNF) secretion, can be extremely important. The use of the lowest possible GC dose, at night, and for the shortest possible time should therefore greatly reduce the risk of infections. Infection is a major co-morbidity in rheumatoid arthritis (RA), and conventional disease-modifying anti-rheumatic drugs (DMARDs) can increase the risk of their occurrence, including tuberculosis. TNF-alpha plays a key role in the pathogenesis of RA, and the data concerning infections in RA patients treated with anti-TNF agents are controversial. Patients and physicians should vigilantly monitor for signs of infection when using anti-TNF agents. Recombinant gene technologies now make it possible to produce protein drugs that are almost identical to naturally occurring human polypeptides, including antibody (Ab) constructs; unfortunately, all human biological agents are potentially immunogenic. An increasing number of recent studies have demonstrated the safety of influenza and pneumococcal vaccines administered to patients with systemic lupus erythematosus (SLE) or RA. These vaccinations are generally immunogenic (i.e., capable of inducing a protective level of specific antibodies) but may not induce an adequate response in a substantial proportion of patients.