The treatment of rheumatoid arthritis (RA) has greatly improved with the use of biological TNF inhibitors (TNFi). These biopharmaceuticals target the inflammatory cytokine TNF, and hereby decrease the autoimmune inflammation, which may otherwise lead to permanent joint damage in the afflicted patients. Although TNFi decrease clinical disease activity in the majority of the treated patients, they are not always effective. Some patients have a partial response, some lose their initial response to treatment, and others never experience effect at all. The concentration of TNFi in the patients' bloodstreams, or the generation of antibodies directed towards the TNF inhibitor (anti-TNFi Abs), are known to have an impact on treatment efficacy. Furthermore, in patients with a good treatment response, strategies for how to tamper or discontinue treatment are lacking. In this PhD thesis, ways to improve treatment with TNFi are explored in three studies. The first study describe current knowledge on the effect of intensifying treatment with TNFi as a way to increase treatment efficacy. The results from this literature review do not convincingly support that intensified treatment increase efficacy in patients with RA in general, although an effect may be seen in patients treated with infliximab. The diverging results on the efficacy of infliximab intensification may be explained by effects on subgroups of patients being masked in mixed cohorts. We suspect that if patients are sub-grouped according to factors such as blood concentration of TNFi or presence of anti-TNFi Abs, an effect of treatment intensification on clinical outcome may bee more convincing. The second study assesses the frequency of anti-TNFi Ab formation in patients with RA in remission in an effort to identify patients for whom continued treatment is superfluous. If anti-TNFi Ab and low drug concentrations in patients in remission are predictors of TNFi-free remission, the impact on treatment and economic costs may be considerable. The finding that 10% of the patients in remission have developed anti-TNFi Abs shows that the potential is substantial. The third study investigates if baseline values of various biomarkers and other variables can predict development of anti-TNFi Abs or the emergence of sub-therapeutic drug levels. From the results, it seems that baseline inflammatory activity, judged from the level of interleukin-6 and possibly C-reactive protein, predicts low drug levels after six months of treatment. This may lead to early identification of patients at risk of treatment failure owing to inadequate drug levels, with the opportunity to take measures to prevent this.