Illegal exploitation of timber in Tanzania is rampant in montane forests. It is mostly done by pitsawyers. To assess the extent of destruction and propose corrective measures, an experiment was laid down in the Machame, Cho me and Rongai Forest Reserves from October 1998 to February 2000. The regeneration potentials of Ocotea usambarensis, Fagaropsis angolensis, Podocarpus falcatus, P. latifolius and Ficalhoa laurifolia were assessed and monitored . Illegal logging was carefully simulated (particularly by reducing felling damage) by felling a single tree in selected experimental plots and subsequent regeneration response monitored. Growth of advance regeneration was also monitored. Litter and soil tillage treatments were applied to selected plots. Canopy closure and the associated light environment in both felled and non-felled plots were quantified quarterly with hemispherical photography. The canopy closure was reduced and the quantity of solar radiation reaching the forest floor was increased by the single tree felling from O to 40% and from 15.1 to 127.8% respectively. Initial results of the experiment after 18 months of observations showed that Fagaropsis angolensis, Podocarpus falcatus, Podocarpus latifolius and Ocotea usambarensis had the potential of regenerating in situ. In general, single tree felling had moderate influence on regeneration of the studied species. A combination of felling and litter/tillage significantly (F = 11.58, p < 0 .05) influenced regeneration of Ocotea usambarensis at Machame. Chome Ocotea usambarensis new regeneration was significantly affected by tree removal (to.05 = -3 .02, p = 0.0051). Ficalhoa laurifolia neither responded to applied treatments nor had advance regeneration. Neither litter nor tilling had significant effects on the regeneration of any target species. Height growth of advance regeneration was influenced to a different extent by the applied treatments and time of application. In most cases, advance regeneration in felled plots grew faster than in un-felled plots. There was a significant effect for Ocotea usambarensis (F = 2.04, p = 0.048) at Machame, Podocarpus latifolius (F = 3.45, p = 0.002) at Chome and Fagaropsis angolensis (F = 94.78, p = 0.000) at Rongai. Increased direct light due to single tree felling had positive influence on Ocotea usambarensis advance regeneration at Machame in March 1999 - May 1999 and September 1999 -February 2000 growth phases (F = 4.72, p = 0.031 and F = 10.31, p = 0.002 respectively). It has been shown that height increment in Ocotea usambarensis at Chome and Machame and Podocarpus latifolius at Chome depends on the initial advance regeneration height (F = 13.41, p = 0.0 15; F = 4.49, p = 0.035; and F = 4.02, p = 0.049 respectively). In almost all sites advanced regeneration growth differed significantly between growth phases. The significance levels ranged from p = 0. 007 to p = 0. 000. It is suggested that the state of knowledge uncovered by this study should be extended and studies on the regeneration potential of economic tree species in other natural forests in Tanzania be conducted.