Teaching effectively online has many challenges, but has the potential to broaden the pool of students. For our fully-online animal physiology lab, we identified teaching objectives related to understanding: 1) how physiological transducers are used, 2) physiological studies, and 3) organ system function. The 6-7 week, two-credit online course we developed has three components. For component 1, students purchase, construct, program and use an Arduino-based system to record EMGs. They design a well-controlled experiment using their system and submit a report. In component 2, online groups collaboratively write a NSF-style proposal to study an aspect of physiology not currently understood. They must choose a topic, review literature, and define questions. Proposals include a budget and human subjects/animal use permission forms as appropriate. With a half-time TA per 50 students, it is possible to give substantial student feedback at each step of components 1 and 2. In component 3, pre-lab modules and quizzes prepare students for ten 45-min simulation labs developed in collaboration with Labster Inc. Post-lab quizzes assess understanding of the following simulation topics: thermal homeostasis and energetics, the ionic basis of action potentials, using voltage and current-clamp to understand nociceptor function, the hormonal control of reproduction , mechanics of skeletal muscle fiber types, autonomic control of smooth muscle, cardio-respiratory function during human exercise, diving physiology of Weddell seals, glucose transport by the small intestine, and renal salt and water regulation. While some hands-on skills available in our in-person lab are missed, the focus of the online lab is on understanding techniques of measurement and quantitative analysis. In particular, we emphasize understanding of the scientific process.