Most physiologically induced examples of recruitment of brown adipose tissue (BAT) occur as a consequence of chronic sympathetic stimulation (norepinephrine release within the tissue). However, in some physiological contexts (e.g. prenatal and prehibernation recruitment), this pathway is functionally contra-indicated. Thus, a non-sympathetically mediated mechanism of BAT recruitment must exist. Here we have tested whether a PPAR activation pathway could competently recruit BAT, independently of sympathetic stimulation. We continuously treated primary cultures of mouse brown (pre)adipocytes with the PPAR agonist rosiglitazone. In rosiglitazone-treated cultures, morphological signs of adipose differentiation and expression levels of the general adipogenic marker aP2 were manifested much earlier than in control cultures. Importantly, in the presence of PPAR agonist the brown adipocyte phenotype was significantly enhanced: UCP1 was expressed even in the absence of norepinephrine, and PPAR expression and norepinephrine-induced PGC-1 mRNA levels were significantly increased. However, the augmented levels of PPAR could not explain the brown-fat promoting effect of rosiglitazone, as this effect was still evident in PPAR-null cells. In continuously rosiglitazone-treated brown adipocytes, mitochondriogenesis, an essential part of BAT recruitment, was significantly enhanced. Most importantly, these mitochondria were capable of thermogenesis, as rosiglitazone-treated brown adipocytes responded to addition of norepinephrine with a large increase in oxygen consumption. This thermogenic response was not observable in rosiglitazone-treated brown adipocytes originating from UCP1-ablated mice; hence it was UCP1-dependent. Thus, the PPAR pathway represents an alternative, potent and fully competent mechanism for BAT recruitment, which may be the cellular explanation for the enigmatic recruitment in prehibernation and prenatal states.