The purpose of the present study was to evaluate the reproducibility and sensitivity of the membrane filter technique by comparing fungal occurrence in two cultivated field soils. The soils were cultivated organically or conventionally but were otherwise similar. The results of the investigation showed high sensitivity and good reproducibility using 0.5mg soil on the filters, while 1.0 mg caused a severe masking effect. At both sampling times the estimates of hyphal lengths were greater in the organically cultivated soil (mean values between 340 and 360m g^-1 dry soil) than in the conventionally cultivated soil (mean values between 100 and 200m g^- dry soil).