National Centre for Scientific Research, Demokritos (NCSRD) 1 article published in JoVE Biology Quantitative Analysis of Aspergillus nidulans Growth Rate using Live Microscopy and Open-Source Software Alexandros Athanasopoulos1,2, Ada Biratsi1, Christos Gournas1, Vicky Sophianopoulou1 1Microbial Molecular Genetics Laboratory, Institute of Biosciences and Applications, National Centre for Scientific Research, Demokritos (NCSRD), 2Light Microscopy Unit, Institute of Biosciences and Applications, National Centre for Scientific Research, Demokritos (NCSRD) We present a label-free live imaging protocol using transmitted light microscopy techniques to capture images, analyze and quantify growth kinetics of the filamentous fungus A. nidulans in both submerged cultures and solid media. This protocol can be used in conjunction with fluorescence microscopy.