Several human worldwide diseases like obesity, type 2 diabetes, hepatic 
steatosis, atherosclerosis and other metabolic pathologies are related to the 
excessive accumulation of lipids in cells. Lipids accumulate in spherical 
cellular inclusions called lipid droplets (LDs) whose sizes range from fraction 
to one hundred of micrometers in adipocytes. It has been suggested that LDs can 
grow in size due to a fusion process by which a larger LD is obtained with 
spherical shape and volume equal to the sum of the progenitors' ones. In this 
study, the size distribution of two populations of LDs was analyzed in immature 
and mature (5-days differentiated) 3T3-L1 adipocytes (first and second 
populations, respectively) after Oil Red O staining. A Monte Carlo simulation of 
interaction between LDs has been developed in order to quantify the size 
distribution and the number of fusion events needed to obtain the distribution 
of the second population size starting from the first one. Four models are 
presented here based on different kinds of interaction: a surface weighted 
interaction (R2 Model), a volume weighted interaction (R3 Model), a random 
interaction (Random model) and an interaction related to the place where the LDs 
are born (Nearest Model). The last two models mimic quite well the behavior 
found in the experimental data. This work represents a first step in developing 
numerical simulations of the LDs growth process. Due to the complex phenomena 
involving LDs (absorption, growth through additional neutral lipid deposition in 
existing droplets, de novo formation and catabolism) the study focuses on the 
fusion process. The results suggest that, to obtain the observed size 
distribution, a number of fusion events comparable with the number of LDs 
themselves is needed. Moreover the MC approach results a powerful tool for 
investigating the LDs growth process.