Fungal molecular biology has benefited from the enormous advances in understanding protein–protein interactions in prokaryotic or eukaryotic organisms of the past decade. Tandem affinity purification (TAP) allows the enrichment of native protein complexes from cell extracts under mild conditions. We codon-optimized tags and established TAP, previously not applicable to filamentous fungi, for the model organism Aspergillus nidulans. We could identify by this method the trimeric Velvet complex VelB/VeA/LaeA or the eight subunit COP9 signalosome. Here, we describe an optimized protocol for A. nidulans which can also be adapted to other filamentous fungi.