Effects of temperature, humidity, temperature and humidity interaction and host on morphometric variability of Paratrichodorus rhodesiensis were studied. Nematode cultures were established in a glasshouse under controlled environments. Amongst the factors investigated, host was found to be the most influential on both sexes (P < 0.05) affecting all characters in females and eight out of 11 characters in males. Ratios b and c were found to be highly variable and hence their use is not suggested. On the contrary, ratio a was found to be a good indicator of nematode condition, particularly in association with hosts. Vulva position (V) was found to be the most stable character. Paratrichodorus rhodesiensis was affected by higher temperatures of 34 and 36°C. Change in humidity did not show a demonstrable trend on morphometric characters in both sexes. Interaction effect of temperature and humidity resulted in a significant effect on body length and body diameter in females and on ratio b and c, pharynx, onchiostyle and tail length in males.