The Kiessig fringes and Bragg reflections of samples consisting of 28 monolayers of magnesium stearate were recorded with a time resolution of 10 s during heating scans from 25 to 62 degrees C with a rate of 0.5 degrees C/min using synchrotron radiation and a linear gas detector. Deposition of the Langmuir-Blodgett films on glass tubes obviates the need for angular scanning of the samples. The multilayer spacing and total film thickness could thus be monitored simultaneously. At 52 degrees C a phase transition with coexisting initial and final states was observed.