This paper describes a study aimed at expanding research on the interactive effect of readers' prior knowledge and text coherence on learning by introducing a third variable, topic interest, which is, the readers' relatively stable affective orientation toward a topic. The hypothesis was that the inferential processes required to fill in information gaps cannot be activated by prior knowledge, topic interest, and their interaction. High school students (n=160) were selected from a wider sample on the basis of their levels of prior knowledge and topic interest to make up 4 groups: (1) high knowledge with high interest; (2) low knowledge with low interest; (3) high knowledge with low interest; and (4) low knowledge with high interest. Students in each group read one of three versions of a scientific text about the greenhouse effect, which differentiated regarding cohesion level. They then carried out four tasks aimed at tapping both superficial and deeper levels of text understanding. It was expected that high-knowledge and high-interest readers would perform best regardless of text coherence, and high-knowledge and low-interest readers would perform better with globally coherent text, as would low-knowledge and high-interest readers. Low-knowledge and low-interest readers were expected to perform worst, especially with minimally coherent text. Results substantially confirm the hypothesis and show the complex interaction between cognitive and affective aspects on learning from text. When prior knowledge is low, topic interest can compensate for it and may help text understanding at text base level. When prior knowledge is high, high topic interest may help understanding at the level of text base. In two of the four tasks, the high-knowledge and high-interest group, which performed best in all tasks, benefited more from reading a minimally coherent text, but in general, the other groups scored highest reading a locally and globally coherent text. Future research questions and educational implications are outlined. (Contains 5 figures, 2 tables, and 27 references.) (Author/SLD)