Abstract. Aim was to look for atrial depolarisation abnormalities in paroxysmal lone atrial fibrillation (AF) patients. 18 AF patients without structural heart disease and 18 healthy controls were included. A 33-channel MCG over the anterior chest and orthogonal 3-lead ECG as a comparative method were recorded simultaneously in magnetically shielded room. Data of 5 minutes was digitised and averaged using atrial wave template. Averaged data was filtered with 40 Hz high-pass filter and the duration of the filtered signal (Pd) was measured automatically. Root mean square amplitudes of the last 60 ms of atrial signal were determined (RMS60). Variation in Pd between channels was described as dispersion index, calculated as Pdi=SD/Pd*100. By MCG Pdi was large (p=0.003) and RMS60 was lower in patients (p=0.02). Group means of Pd were comparable (104 and 106 ms), but the longest as well as shortest Pd were measured in patients, paralleled with a greater SD value. In paroxysmal lone AF, the high frequency components of the last portion of atrial signal are reduced and the variance in duration of atrial depolarisation is substantial, suggesting pathology in the left atrium. MCG appears to be sensitive non-invasive method to study atrial electrofysiology in AF.