This study presents and interprets some conceptual difficulties junior-level physics students experience with Ampère's law. We present both quantitative data, based on students' written responses to conceptual questions, and qualitative data, based on interviews of students solving Ampère's law problems. We find that some students struggle to connect the current enclosed by an Ampèrian loop to the properties of the magnetic field while some students do not use information about the magnetic field to help them solve Ampère's law problems. In this paper, we show how these observations may be interpreted as evidence that some students do not see the integral in Ampère's law as representing a sum and that some students do not use accessible information about the magnetic field as they attempt to solve Ampère's law problems. This work extends previous studies into students' difficulties with Ampère's law and provides possible guidance for instruction.