Rare-earth elements (REE) were investigated by neutron-activation analysis in nine apatites and seven coexisting plagioclase cumulate minerals at three different levels of the Bjerkrem-Sogndal layered lopolith (Rogaland, S.W. Norway), a massif which displays the complete andesine anorthosite-charnockite series of rocks. The REE (except Eu) behave as hygromagmatophile elements (as defined by Treuil) in the course of the fractional crystallization process which has given rise to the massif. The concentration is indeed inversely proportional to F, the fraction of residual liquid. This characteristic permits placing an upper limit to the value of the partition coefficients of REE between apatite and magma. They must approximately be equal or less than 5. The apatite-plagioclase distribution coefficients show little variation during differentiation. This can be explained by an open system crystallization of the intercumulus liquid and permits calculating the plagioclase-magma partition coefficients. Values similar to those of Paster et al. (1974) are obtained. A range of possible D Eu apat is calculated, together with the corresponding D Eu plag at three different levels of the intrusion. Drake's (1975) geobarometer based on Eu in plagioclase is used to estimate the fugacity of oxygen. There is good agreement with the values obtained with the Buddington and Lindsley geobarometer. A continuous decrease of ƒ o 2 throughout the whole sequence cannot be invalidated. REE were also determined in apatite from five FeTi oxide ore-bodies occurring in the same magmatic province. The consistency between the trace element behaviour in the oxides and the REE in the apatite permits identifying fractional crystallization as controlling the generation of the ore-bodies.